As it's pictured on the main page, a young woman and an older teen (and later, a young teen girl) take up the role in Kyojin no Hoshi:
Hyuuma Hoshi's older sister Akiko has to play this role, since her and Hyuuma's mother Harue died very young and their father Ittetsu is a less-than-ideal one to them. As such, she is Hyuuma's biggest supporter and is gently yet firmly protective of him, willing to go against Ittetsu and others if it means she'll be able to help him.
Hyuuma's Friendly Rival Housaku Samon is the eldest of six orphaned siblings — the others are his three brothers (Seiichi, Masahiro and Jirou) and his two sisters (Chiyo and Michi). Their father died when Hosaku was in fourth grade and their mom followed suit; they were forced to work in their uncle's farm afterwards, until Housaku got a scholarship to a good school/team. After all of this, Housaku decides to be a baseball star so he can provide for himself and the children adequately; in Shin, said dream has more or less become true. And there's a big plus in Shin: by these days Housaku is married to his Love Interest Kyouko, who helps him out.
The second eldest of the Samon children, the Yamato Nadeshiko in training Chiyo, does her best to support her elder brother's efforts via mothering their younger siblings when he's not around. She at times even mothers him a little.
In Mazinger Z, even when the Kabuto brothers lived with their grandfather Juuzou after the deaths of their parents, in practice Juuzo was too busy to fully be able to take care of the boys so 16-year-old Kouji was pretty much a parental figure to his 10-year-old brother Shiro. Even when Sayaka's father Gennosuke took the two under his wing, Kouji kept taking care of Shiro as much as possible.
Yukiji looks after her little sister Hinagiku in Hayate the Combat Butler, but usually it ends up being the other way around.
While this may have been true after their parents abandoned them (and possibly even before), it seems that normalcy has reasserted itself after they get adopted by the Katsura's. Yukiji seems to have reverted to more child-like while Hinagiku is supporting herself and generally not truly caring about her older sister except when it makes her look bad.
Minami Shimabara in Neo Ranga, who's been raising her sisters Ushio and Yuushi.
Ralph Werec in Soukou no Strain was promoted to parent of his much younger sister Sara after the death of their parents, James and Annie. This fostered an enormous sense of Big Brother Worship in her, which makes it even more painful when he leaves to join the army and comes back as an Omnicidal Maniac.
Sara herself plays a similar role to Emily.
In Fullmetal Alchemist, Ed's as much of a father to Al as he is an older brother. And in both a light novel and the first anime, the alchemist Russell Tringham takes care of his little brother Fletcher.
Seto Kaiba of Yu-Gi-Oh, who promised himself when he was 10 that he would be a father to his brother, Mokuba, after their parents died. Aside from his Noble Demon personality and Agent Scully views, Seto has been good to his word. Mokuba uses the highest, most respectful honorific toward him, "Nii-sama."
Although when they first turned up in the manga Mokuba was an evil, cheating little creep who attempts Yuugi and Jonouchi's murders, and then an example of how evil Seto was, since while Mokuba is crying and saying he just wanted 'Seto-sama's' approval Seto says things like 'In the world of games, there's no place for brotherly affection! Until you understand this, you'll never be anything but a loser!' and proceeds to put him in the mindcrush-simulation box that has already caused heart attacks and breakdowns, since those were the terms of loss. Yuugi rescues him, of course. Then Yuugi (or better said, Yami Yuugi) mindcrushes Seto again, and when he gets his heart-puzzle back together and finishes his second round of catatonia, he loves Mokuba again from that point on. And the kidnappings begin.
Jun Manjyome's older brothers on Yu-Gi-Oh GX are the closest thing to parents he appears to have, constantly putting pressure on him to uphold the family honor. Too bad they're Corrupt Corporate Executive jerks.
In a filler arc of the original TV series, Kaiba's Unknown Rival Siegfried is implied to have raised his younger brother Leon, or at very least taught him how to play card games. Jounouchi even calls him a Stage Mom.
Brock from Pokémon is pretty much this trope. He takes care of nine siblings when his parents hit the road. Arguably, he holds the same position within Ash's group as well.
Yuuta from Papa no Iukoto o Kikinasai was just a 19-years-old college freshmen when his older sister asked him to take care of her daughters for a week while she and her husband were gone on vacation... then they died in the air flight. The three girls would be separated into different homes, taken by different family relatives; the girls didn't want to be separated, seeing this dire situation Yuura volunteered to become their guardian; the family agreed, but they're one step away of taking the girls away if the young and stubborn Yuuta fails to raise them properly
Hwang Bu-ling aka Mew Pudding from Tokyo Mew Mew, a victim of Parental Abandonment - her mother is dead, her father left to practice martial arts, and she has five younger siblings to look after. The anime version at least introduced a kind kindergarten teacher who helps her to take care of her little sister. Top it with the fact that Bu-ling herself is only an elementary school student, and prior to the series beginning, she apparently supports her family entirely by doing tricks in a park.
Rika Noyamano of Air Gear definitely qualifies for this, seeing as her parents are gone, as well as Ikki's, the only mention of either ones' parents being that Ikki was left in her care by his parents when she was only a child. Though considering she's gone for months at a time with her Professional Wrestling gig, she might also qualify as a case of Parental Abandonment herself.
Mad Scientist Koumi Lee of D Gray Man is obsessively overprotective of his little sister Lenalee. As befitting the trope, their parents were killed by Akuma before the story.
Amusingly, Cross to Allen when he first found the boy as shown in Chapter 206, where said character admitted to having no idea how to care for a child. Cross eventually learns how to cook and do the laundry, making this more of a promotion to housewife.
Grave of the Fireflies does this in a painfully realistic and tragic manner with the young teen Seita Yokokawa and his infant sister Setsuko, largely because it seems that much of it is a true story - apparently Setsuko was based on the novelist/script writer Akiyuki Nosaka's adoptive sister Keiko, and he wrote the original novel in part as a way to cope with his grief and self-recrimination over her and other loved ones' deaths (another of his sisters died of malnutrition, and his uncle/adoptive dad perished in the bombings of Kobe)
Gantz has a rather tragic example of this trope; not only is Kato basically his young brother Ayumu's parental figure, he ends up dying, thus leaving Ayumo without an adult to look after him.
AIR has Dr. Hijiri Kirishima, who takes care of her younger sister Kano since their Ill Girl mother died after Kano's birth and their also doctor father pretty much worked himself to death.
Touya from Cardcaptor Sakura gets a partial one. Fujitaka actually is a good father, just a very busy one (despite his own wishes) so Touya has to take care of Sakura many times.
Code Geass. After their mother was murdered and their father abandoned them, Lelouch becomes the primary caretaker to his disabled little sister, Nunnally, to the point that making the world a better place for her is one of his main motivations for his rebellion against the Emperor.
Kasumi of Ranma One Half pretty much took the role of the mother in the Tendo-dojo.
Tatewaki Kuno has also taken over in his family- and when his father returns they even fight about it, with Tatewaki refusing to surrender leadership. Koidachi of course favors her father, and it's not like Tatewaki has done that great a job of "parenting" Koidachi, but considering the choices are Tatewaki or his father - it's one of the few times Tatewaki comes off very favorably.
Ichiyō Tsukushima in Cross Game; she's the eldest of four girls and their dad is a widow, so she helps Mr. Tsukushima with her sisters.
In Bleach, Sora Inoue, who is 15 years older than his baby sister Orihime, protects her from their Abusive Parents and runs away from home with her as soon as he reaches legal age, bringing in a paycheck and raising her until his death in a car accident three years before the main plot, at which point Orihime lives on her own with some relatives' financial support. He even lampshades this by saying Orihime is "more like a daughter (to him) than a sister."
Also, Hisana, Rukia's older sister. This is unique in the fact that it was actually Hisana and Rukia who died together and wound up in the afterlife. Unfortunately, that afterlife turned out to be a Crapsack World and Hisana couldn't hack it. She thus abandoned Rukia years before the start of the series, and could never forgive herself for it - therefore right before she died again, she begged her husband Byakuya to find Rukia and give her a normal life... without telling her; it's because of her last wish, and she felt she didn't deserve to be called Rukia's older sister after abandoning her, asking Byakuya to be the family-and older sibling that she never was to Rukia.
Kaien Shiba was this to Ganju and Kukaku. And then when he "died" (seeing a trend here?), Kukaku was this to Ganju.
According to supplementary material, Captain Junshiro Ukitake is the eldest of eight siblings and he supports both his five younger brothers and two younger sisters. It's subtly and hilariously confirmed in the Thousand Year Old Blood WarAnimated Adaptation: a young adult Ukitake asks a just as young Shunsui Kyouraku to give him his monaka pastries, then takes him to his house... and five of the kids, whose ages go from toddler to mid teens, gang up on Ukitake to get the pastries.
In GetBackers, Himiko Kudou is said to have been raised from infancy by her older brother, Yamato, and that he was the one who taught her to use her poisoned perfumes and to work as a thief alongside him from a young age. His murder when she was thirteen is what fuels her grudge against the main character, Ban Mido. Who actually is her real brother. And not to mention, Yamato himself asked Ban to kill him.
In Minami-ke, Haruka takes care of her two siblings Kana and Chiaki. While there is no mention about parental abandonment and their older cousin Takeru comes by once in a while, Haruka is the one who does all parental duties.
Racine in Glass Fleet accredits her tomboy personality and love of swordsmanship to having been raised by her brother, Michel. Even though their father was still alive, he didn't do anything for Racine except try to get her to Stay in the Kitchen.
Haruma from Chocotto Sister gets plunged into this role after he gets his sister Choco as a christmas present.
In a weird example, inverted, Usagi and Chibi-Usa on Sailor Moon have a similar relationship. Chibi-Usa is sent to the past to live with Usagi, who is her mother in the future. However, since Usagi is a teenager, Chibi-Usa loves yet usually has a lack of respect for her as her future mother, and they get into arguments as if Usagi were the sibling substituting for the parent, instead of the future parent.
Black of Tekkon Kinkreet takes care of the playful but peculiar White much like a parent; he steals money to support them both and even helps White dress. (He doesn't know how to do so by himself yet.) Although it's never explicitly stated that they're related, the two are so close that they might as well be siblings.
Mai Tokiha inherited the responsibility of taking care of her sickly younger brother Takumi from first her mother and later her father. This responsibility weighs on her pretty heavily, but she tries not to let anyone know that. She also ends up considering her status as Takumi's caretaker a key part of her identity, so much so that she has conflicting feelings when he expresses a desire to become more independent, and this is part of the reason Yuuichi replaces Takumi as her Key.
In Captain Tsubasa Koujiro Hyuga's Yamato Nadeshiko mother does not want her eldest son to "replace" the family's Disappeared Dad (who died two years before the story started), but Hyuga himself insists in working part-time after school to help out the family. This partially stops when Hyuga becomes a Scholarship Student in Tokyo, but he keeps taking care of the family once he becomes a soccer star: before going to Italy, he buys them a beautiful house in Saitama and sends them money regularly.
Daiichi Yamura from Bokurano takes care of his three younger siblings since his father has been gone for a while. Mr. Yamura is actually helping a friend in distress, not permanently gone. Daiichi dies after his battle, but the boss from his part-time job takes care of the other kids and then Mr. Yamura comes back for them.
Kaori from Best Student Council. Hinted at in the early episodes, near the end we see that she is the oldest of four children, left caring for her siblings after their parents death. She is the only council member not to live at the dorm, preferring to live with her younger siblings in a house in the city, delivering newspapers to make ends meet. She keeps this a secret from the others because she doesn't want to them to feel sorry for her, and gets torn into by Rino for this once it comes out.
Fifteen year old Sumi of Stepping on Roses (Hadashi de Bara wo Fume) is an example of this. Without having her own parents around, Sumi is forced to take on the motherly role for the adopted siblings that her irresponsible older brother Eisuke keeps bringing home with him. This can apply to a lesser extent for Eisuke, though his primary motivation for raising the children is so that he can put them to work for his future business empire.
In Binbou Shimai Monogatari, Kyou takes care of her younger sister Asu after their mother died and their father ran off. It's not always easy for her, since she is still only 15 herself and has to juggle school with work. Still, her love for her sister makes her pull it off.
Michael Garret of Gun X Sword was promoted to parent years before the series began. Up until he is kidnapped by the Claw, he did a good job of caring for his younger sister, Wendy.
Go Katou from Aishite Night has been taking care of his brother Hashizou ever since their father's death. In a subversion, Go's mother Yoko is still alive... but Hashizo's mother is actually the lover of their Disappeared Dad, making little Hashizou a pint-sized Heroic Bastard. Despite Yoko's conflicted feelings on the deal, Go still took the little kid in.
In Eden of the East, Saki's older sister Asako took responsibility for raising her after their parents' deaths. Saki is grateful for her assistance and that of her husband Ryousuke, but is hoping to get a job so as not to rely too much on her kindness.
Kanba Takakura from Mawaru Penguindrum became this to Shoma and Himari when he was around 13 years old. As a child, he promised his father Kenzan that he'd protect his siblings if something ever happened to him and their mother Chiemi. Then it turned out that the parents were members of a terrorist organisation and had to run away from home...
Sakanoue Gammon of Phi Brain Kami no Puzzle has a younger sister, who he supports by submitting puzzles to magazines. He also tries to butt into every one of the Kenja Puzzles set up by the P.O.G. in an attempt to get the prize money and later joins them, though in that case it's not just for the money.
Kurumi from Haou Airen is both the eldest daughter and the main breadwinner of the Akino family, since the father died when she was 14 years old and the mother is a very frail Ill Girl.
In Scrapped Princess, Raquell is more or less forced to play the mother to her bickering younger siblings Shannon and Pacifica after the rest of their household is killed by The Government.
16-year-old Kodaka Hasegawa of Boku wa Tomodachi ga Sukunai is this for 13-year-old Kobato. With their mother Airi dead a few years after Kobato was born, and their father Hayato working in America as an archaeologist, the boy had to raise Kobato by himself, cook her meals, and put up with her vampire-lolita fantasies. Fortunately, Hayato sent them to study in St. Chronica Academy, run by his best friend Tenma Kashiwazaki, whose teenage daughter Sena would fall in love with Kodaka and develop a comically unhealthy obsession with Kobato.
In Brave Police J-Decker, Yuuta Tomonaga's parents are near always off at their archeologist work so his eldest sister Azuki takes the caretaker role for him and their other sister Kurumi.
In Grimm's Fairy Tale Classics, the series' take on Bluebeard implies that Josephine and the youngest of her three brothers were raised by the eldest two.
Brother and Sister has Rosa/Sister 'mothering' her younger brother Rudolf whether as a human or a stag, asking her future husband the King to let her take him with them to live in the palace.
Kyou Kara Yonshimai has the 27-years-old Office Lady Botan Manabe raising her three younger sisters (19-year-old Kashiwa, 12-year-old Momiji and The Protagonist, 15-year-old Sakura) after their father runs off following their mother's death. She ends up cracking under the pressure and, after a big fight with her sisters, she runs away too, so Kashiwa has to step in and take her place as the family's breadwinner. However, at the very end the girls get a phone call that it's all but stated to be from Botan, implying that she'll return or at least retake contact with them. . .
Kashiwa herself does her best to take care of Sakura and Momiji, and as a bonus she's the one in charge of the household (and especially food) as Botan works. As said above, when Botan leaves she begins to work (apparently, also as an Office Lady) to support herself, Momiji and Sakura.
In The Brave Express Might Gaine, Sally Yoshinaga's mother is unaccounted for and her father is severely ill so Sally must take up part-time jobs to take care of her dad, her brother and herself.
In Demon Slayer: Kimetsu no Yaiba, the main character Tanjiro Kamado took up the "breadwinner/man of the family" role one year before the story started, due to his father Tanjuro's death of illness. The sister that came after him, Nezuko, helped him and their mother Kie as much as she could by taking care of their younger siblings, especially the toddler-aged Rokuta. And then everyone in the family save for Tanjiro and Nezuko were killed, so Tanjiro must finish raising himself AND Nezuko (whose mind has receeded to that of a little girl after being turned into a demon) while fighting all kinds of demons. . .
The two Upper Rank 6 among the Twelve Kizuki, Gyutarou and Ume/Daki, were the children of a very abusive woman, and after she died a teenage Gyutarou raised his pre-teen sister by himself. . .
Sanemi "Wind Hashira" Shinazugawa did what he could to help his mother Shizu and his siblings (including the brother after him, Genya) after the death of the abusive family patriarch Kyougo. He and Genya are seen working together in the streets, talking about how Sanemi has become "the man of the house". And then Shizu was turned into a demon, and not unlike in Tanjiro's case, everything went South for him and Genya aka the two survivors. . .
In My Hero Academia, Tsuyu "Froppy" Asui's parents Ganma and Beru work full-time so she's had quite a part raising her younger siblings, Samidare and Satsuki.
After the Todoroki family dynamics went to shit due to the patriarch Enji's increasing obsession with Superpowerful Geneticsand the matriarch Rei had to be committed to a mental hospital as a consequence of all of this, a good part of Shoto's raising was in the hands of his older sister Fuyumi.
In Kotetsu Jeeg, Dr. Senjirou Shiba was so estranged from his family due to his work and investigation of the Yamatai Kingdom that in practice, his eldest son Hiroshi aka The Protagonist was the "man of the house" and helped his mother Kikue raise his little sister Mayumi. When Dr. Shiba died in Hiroshi's arms, he not only took up fighting the Yamatais as Jeeg but continued supporting his mom and sister as much as he could.
