Hates Being Alone

Loneliness is a disease that can lead to death. They might as well be the same thing. —Holo, Spice and Wolf

This is when a character just can't seem to bear the thought of being left alone under any circumstances. Whether it be from a Friendless Background or a belief that Loners Are Freaks, he or she may frequently want to be assured they are not alone by others, such as by seeking out company the moment they realize they're by themselves. Ironically, these characters still tend to lack friends for some reason or feel the effects of solitude despite all their efforts not to. Since they are not usually isolated by choice, they will often hate Eating Lunch Alone, will probably never use the phrase Leave Me Alone! (although saying Please Don't Leave Me is certainly likely), and may even prefer walkingAlone in a Crowd rather than staying at home and being reminded they have no one to talk to or hang out with. In cases where the character does have either a Limited Social Circle or only one friend, expect them to cling to any of their friends (including pets/plants/inanimate objects) like a lifeline in order to escape their feelings of desolation.

Characters who have experienced severe isolation, Parental Abandonment, All of the Other Reindeer, or one of the obvious downsides to immortality can often develop into this. Shy characters can fall victim to this as well. May lead to a case of Lonely Together, if the character finds nobody but other lonely people for company. It also tends to be a common justification for I Just Want to Have Friends. Contrast The Hermit or any introvert for that matter.

Anime and Manga

• Bleach: Coyote Stark is the embodiment of loneliness.
• Fairy Tail: Lucy Heartfilia grew up without friends, was neglected by her father, and lost her mother at a young age. She had nobody to talk to throughout most of her childhood except her Celestial spirit Aquarius who treated her poorly most of the time. One reason why she puts up with the crazy wizards at her guild is because they're the closest friends she's ever had.
• Fruits Basket:  Akito Sohma fears being alone/abandoned so much that he rules the Zodiac by fear to keep them from leaving. The whole "being forced to live as a guy" thing probably doesn't help much, either.
  • Akito can be seen as a deconstruction, as he's a good example of what an overwhelming fear of being alone could actually do to someone, and the lengths they'll go to in order to prevent it.
• Issei Hyoudou of High School D×D, most obviously when he can't sleep properly without someone else in the bed. Despite his usual bedmates being his stonking hot King Rias Gremory and hopelessly lovestruck Asia Argento, and his status as a Lovable Sex Maniac, this isn't sexual. Past experiences and deeply-buried but crushing self-worth issues mean waking up alone and thinking he'd dreamed all the girls around him is a terrifying thought he never completely gets over.
• The eponymous character of Inuyasha eventually develops into this, to the point that loneliness is revealed to be his greatest fear in a filler episode.
• Mirai Nikki: Yukiteru Amano and Yuno Gasai both have this problem. Yuki grew up without any friends since he was too scared of getting hurt and has been neglected by both his parents, while Yuno was abused and neglected by her father and mother, respectively, and ended up accidentally killing them. As a result, they are both very lonely and desperate for someone to fill the void, especially Yuno, who's so scared of losing Yuki that she's willing to kill anyone who gets close to him.
• Naruto: Naruto Uzumaki grew up deprived of any friends or much familial support, so he often tries drawing excessive attention to himself by causing all kinds of mischief to make people notice him. He is also quite close to Iruka because he was the only person who was friendly to him in Konohagakure (before making more friends).
• Neon Genesis Evangelion: Most of the cast have abandonment issues. One of the series' overhanging themes is that people are afraid of being alone but they are also afraid of being hurt by others. Shinji and Asuka are especially prone to this behavior and serve as the series' crowning examples. According to supplementary material, the reason that Asuka returned to the real world alongside Shinji at the end of End of Evangelion was because he needed her above all, even if they had hurt each other.
• Shakugan no Shana: Shana fought for years with only the bodiless Alastor for company. She meets Yuji and gradually falls in love with him. At one point, she fights a monster by herself. Yuji shows up right as she wins. Shana cries against him and says it now hurts whenever she's alone.
• Holo from Spice and Wolf (quoted above) is characterized by an intense fear of loneliness due to the hundreds of years she spent in solitude while watching the humans around her grow old and die. To her, there is no difference between loneliness and death.

Literature

• The Demonata: Kernel Fleck had been a loner his entire life, but it didn't bother him when he was younger. One day, however, this changed and by the time Demon Thief begins he doesn't like being alone anymore.
• Jack Reacher: Inverted with the title character. Not only does he like being alone, he goes out of his way to be left alone. This is due to his years of service as a United States Police Corps; he has seen the absolute worst of what society has to offer, and he never wants to back to that again. Doesn't stop him from accepting any call for help, however.

Live-Action TV

• Doctor Who has this as one of the primary character traits of the Doctor, right back from the very first days — the First Doctor has a Heroic B.S.O.D. in "The Massacre" when he thinks his companions have all left him to continue wandering the cosmos alone. While the degree to which the Doctor hates being alone — and the reasoning why — fluctuates between incarnations (some mourn the loss of a Morality Chain, others find solo travel pointless and boring, others get insecure without constant attention, etc.), the stories where the Doctor has no official companion invariably go Darker and Edgier and show the Doctor performing much more morally questionable actions — "The Deadly Assassin" (Fourth), "The Waters of Mars" (Tenth), and "Heaven Sent"/"Hell Bent" (Twelfth) are particularly extreme examples.
• Friends: It's hinted Chandler is this. When Joey moves out he's openly distressed and quickly finds a new roommate despite admitting he can afford his apartment by himself. He also worries that all the other friends will get married and leave him behind, begging to be allowed to come over for holidays when this happens. This probably stems from his unorthodox and neglectful parents, who divorced when he was a child and sent him to boarding school, so the friends were the first stability he'd ever known.

Chandler: You'll see, you guys are all gonna go off and get married, and I'm gonna end up alone. Will you promise me something? When you're married, will you invite me over for holidays?

• Sherlock: Ironically, even though Sherlock never knew what it was like to have friends, when he met John, he didn't want to be alone again. As in, he didn't want to be abandoned by him, and even if he didn't, he didn't want him to get killed. John is this, too. Before he met Sherlock, he was so alone, and-yeah.

Video Games

• Fire Emblem Fates: Kana, the Avatar's child, has this trait. As with all the second generation characters, their parents had to hide their kids safely in a Pocket Dimension, to prevent monsters from killing them. Kana apparently was hit the hardest by this, as seen at the end of their recruitment chapter. The Avatar doesn't think Kana is ready for combat, and decides to leave him/her behind after giving them their dragonstone to control their ability to transform into a dragon. Kana then tearfully begs to join the party, saying they really want to go along with the Avatar, and that they hate continuing to wait while thinking the Avatar may never return. The Avatar apologizes, having had no idea that their child felt this way from the beginning. Kana then joins the party.
• League of Legends: All Yordies have this trait.
• Mass Effect: Implied to be the case with Commander Shepard since the soldier has gained allies who're his/her True Companions and the thought of them separating doesn't feel the same. In a conversation with Javik, he/she states that without the affection of his/her crewmates, all he/she has in his/her life is death, which isn't enough.