In bad fanfiction (especially of the Jerk Sue or Sympathetic Sue kind), one EXTREMELY common plot device is to make the parents of one of the characters physically, emotionally, sexually and/or mentally abusive, to throw said character in the arms of his/her True Love.
Heck, even doujinshi use this cliché. In one of NEGAHYST Circle's The Prince of Tennis dj, both Masaharu Niou and his mother are routinely abused by Niou's alcoholic father (with said alcohol problems being nwhere found in canon since we barely know about niou's parents), and it's used as a flimsy plot device to make Niou Wangst and throw him in his partner Hiroshi Yagyuu's arms.
Crossover Fics[]
KaguyaKozuki of Metroid: Kamen Rider Generations Vol. 3: Fates Intertwined is an Expy of Ragyo Kiryuin, who takes this trope to a whole new insane level that made even Banno and Masamune look like docile lambs. Kaguya was not only physically and emotionally abusive to her own daughter, Sayaka; she even subjects her to constant sexual abuse. She even treats her own husband Ryohei like crap; seeing both of them as objects of gratification than an actual family stemming from her pettyjealousy towards Takumi Katsuragi. It's made even worse when she brainwashes Misora using Evolt's alien powers into making the latter her submissive daughter, to the point she turns her into a Sex Slave.
Kill la Kill[]
In Cellar Secrets, this is played with in Ragyo's case. While neither Satsuki nor Nui gets the worst of her treatment, she does seem to abuse them psychologically and lorded over them with fear [1]. However, at the same, she was exceptionally cruel to Ryuuko, keeping her caged and isolated in the titular cellar and, apparently, physically abusing her. She does regret her treatment of her daughters and, as she dies, tells them she loves them, however, she acknowledges she can do nothing to atone.
In Kill la Kill AU, we have Ragyo's mother, Youko, in that she even stated she wished she never had her, states that she should have thrown her away, ignores her in favor of sitting in front of the TV and smoking cigarettes, and even cites her daughter's birthday it as the day where her life was ruined when she was only six years. Needless to say, after Ragyo is struck by a car, her parents divorce and her father takes full custody of her. Likewise, Ragyo herself is a subversion, as she's shown to be very loving towards her children.
While they're not her real parents, One More Time, One More Chance makes Ryuuko's foster parents these, as she was sent out to pretty bad homes. It's not clear what they did but, one chapter, had her wondering about "creepy people" and another chapter mentions she was kept as "entertainment".
We have this in Kiryuuin Chronicles with Satsuki's step-father when he snatches her out of the closet (where she was hiding the night before) and throws her into a wall. This was after he had beaten her mother and her Parental Substitute.
In The Outside, while not a parent but a sibling and generally meaning well (but very misguided), Satsuki is a downplayed case of this, as, she could be pretty strict with her rules and how she enforces them. According to parenthesis, her answer to Ryuuko not eating all of her food was to glue her to the chair (literally). From what we got in chapter 27, her response to Ryuuko wetting the bed was to make her take a cold bath and, in chapter 35, we find out that the worst she's done so far was pull a then-3-year-old Ryuuko's hair and give her pinches. Besides the aforementioned three, we can assume her punishments for Ryuuko were mainly benign. However, while she doesn't mean any harm by it, her treatment does have its effect on Ryuuko mentally, as the latter feared breaking her rules for some reason or another.
Memory's Note:Ragyo being this is why Satsuki took her then toddler sister and ran away from home.
Naruto[]
Pick any Naruto fan-fiction where Hiashi Hyuuga is a main or supporting character. In 90% of those works, he's shown as being verbally, psychologically, emotionally, and sometimes physically abusive toward Hinata; Team 8 is one example of all four types in action in the same story. [2]
Neon Genesis Evangelion[]
Nobody Dies, a Neon Genesis Evangelion fanfic, features Kyoko Zeppelin Sohryu, who in this continuity was not driven insane by the contact experiments. She emotionally abuses Asuka, turning her into a Shrinking Violet, rather than the Jerkass that Asuka was in the series. In an interesting semi-aversion, Kyoko realizes her mistakes when the other NERV personnel nearly murder her for it, and resolves to try to become a better person. She and Asuka are now on at least amicable terms.
RWBY[]
RWBY fanfics that aim to give Cardin Winchester character development will saddle him with an abusive father on top of a dead mother who loved him very much.
Since the viewer is given no information about Pyrrha Nikos's parents (other than a woman implied to be her mother speaking to Jaune in volume 6), some fics portray them as Stage Parents who pressure her to be perfect all the time to explain her skill levels and isolation angst. Sometimes this even extends to physical abuse.
YU-Gi-Oh![]
Son of Apophis, a Yu-Gi-Oh! fanfic, takes the abuse Marik experiences to a whole new level. His father actually attempts to mute him.
Touhou Project[]
In Gensokyo 20XXI, while not her mother, at least technically, Kanako clearly fits in that she would beat Sanae to vent frustrations and over minor infractions. It was noted throughout the rest of the series that, while she regretted abusing her, she didn't get a chance at redemption, as Sanae had died [3].
↑(i.e., her beating her secretary and leaving them to see her injuries and the fact that they don't refer to her as "mother")
↑(Ironically, the remaining 10% tend to portray him the way he was and currently is in canon—emotionally distant, but not such a bad guy once Character Development sets in.)
↑(before being brought back from the dead through Yukari's reality-warping in 20XXIV)