The Girl in the Library: Until The Pure You Falls From Grace

The Girl in the Library: Until the Pure You Falls From Grace (Toshoshitsu No Kanojo ~Seiso Na Kimi Ga Ochiru Made~) is a short manga series written by Arare Ame and adapted into a four-episode OVA by Pink Pineapple.

The story begins when a high school student, Yukiha Serizawa, while working as a library assistant with her crush, Aida, defends the janitor, Masami Kitou, after he's accused of breaking a vase. Masami, in turn rapes her while she's drugged while recording it and then blackmails her into being his sex slave. However, Masmai proves to be really good at sex which Yukiha begins to enjoy and eventually becomes his sex slave of her own free will.

Tropes used in The Girl in the Library: Until The Pure You Falls From Grace include:

Abusive Parents: Both Yukiha and Masami will become this. Masmai plans to rape his child if it's a girl or abort it if it's a boy, and Yukiha's become too much of a slut to care.
All for Nothing: The entirety of episode/chapter 2 is this, with Masami refusing to delete the sex video he made even after Yukiha humiliated herself.
The Bad Guy Wins: Masami not only gets away with raping Yukiha over and over, but she becomes his sex slave of her own free will.
Bigger Is Better in Bed: Sadly Masami is this trope which played a role in Yukiha becoming his sex slave willingly.
Blackmail: Masami threatens to release a sex tape he made when he raped Yukiha if she doesn't agree to be his sex slave.
Break the Cutie: Yukiha, a kind-hearted girl is repeatedly raped by the janitor and becomes so corrupted she becomes almost as bad a person as he is.
- Also Aida, a kind-hearted boy suffers an immense mental breakdown after the girl he loves dumps him for her own rapist.
Child by Rape: Averted, Yukiha becomes pregnant after she becomes Masami's sex slave willingly.
Defiled Forever: Masami took Yukiha's virginity when he raped her. Because of that she felt unworthy of Aida's love.
Derailing Love Interests: Played darkly here, Aida is a very friendly person but his poor sexual performance made Yukiha dump him for Masami.
Despair Event Horizon: Aida after Yukiha not only has sex with Masami while he watches on his phone but mocks his poor sexual performance. Even after six months, he's still not only traumatized, but became a shut-in with garbage piling up in his room.
Downer Ending: Episode 4 ends with Aida completely heartbroken, Yukiha presumably disowned by her parents, her reputation in school shattered and pregnant with Masami's child, whom he plans to rape if it's a girl and abort if it's a boy.
Karma Houdini: Masami gets away with his actions and gains Yukiha as a sex slave.
The Farmer and the Viper: Yukiha's reward for saving Masami from being fired over a vase is to be raped and used as a sex slave through blackmail.
Face Heel Turn: Yukiha was corrupted by Masami's sexual prowess and became just as evil as he was by Chapter 5.
Fan Disservice: Masmai is a well-endowed sex god. But he's also an ugly bastard with hairy legs and is possibly in his 50s and is also a vile rapist.
Faux Affably Evil: By chapter 5, Yukiha maintains a sweet and almost innocent personality, but assists Masami in raping her teacher, Takamine, showing she has become just as evil as he is.
Good People Have Good Sex: Unfortunately averted. Though Aida loves Yukiha, his poor performance in bed makes Yukiha dump him for her own rapist.
Happiness in Slavery: Yukiha becomes too dependent on Masami to sexually pleasure her that she becomes his sex slave willingly.
Humiliation Conga: In episode/chapter 2, after raping Yukiha, Masami tells Yukiha he'd consider deleting the sex video on his phone if she'd place bondage straps under her school clothes with a vibrator jammed in her for the day. Whenever the teachers would call for her, Masami, watching through hidden cameras would activate the vibrator. When Aida confessed his love for Yukiha, Masami activated the vibrator before she could confess her love for him as well. In the end, he refused to delete the video.
"It's Not Rape If You Enjoyed It": Yukiha starts to enjoy sex with her rapist and dumps Aida for failing to pleasure her.
Making Love in All the Wrong Places: More like being raped in all the wrong places. Masami has raped Yukiha in the school library and a public restroom and didn't stop even when another person entered.
Naked Apron: Yukiha wears it after being becoming Masami's sex slave willingly. Also she's pregnant while wearing it.
Netorare Genre: It begins near the end of episode/chapter 3 and goes into full force in episode/chapter 4 when Yukiha has sex with Masami of her own free will while openly mocking Aida as he watches.
Nice Guy:Aida, often helping Yukiha at the library and vowed to protect Yukiha from Masami.
No Pregger Sex: Very averted. Masami even recorded it saying he'd be paid a lot of money for a sex video with a pregnant high schooler.
I Have No Daughter: It's strongly implied that Yuika's parents disowned her when she ran off with Masami and sex tapes about her were leaked. Not like she cares though.
I Showed Her What A Real Man Is: Masami mocks Aida when Yukiha becomes his sex slave willingly.
I Was Quite a Looker: Backstories in the manga suggest Masami was quite handsome when he was much younger.
I Will Protect Her: Aida vows to protect Yukiha from Masami. It goes very wrong.
Official Couple: Yukiha and Masami, unfortunately.
Oh Crap: Yukiha does this twice. In chapter/episode 2, when she realizes Masami never planned to delete the sex tape even after she humiliated herself and again in chapter/episode 3 when she learns Masami knows where she lives.
Parental Incest: Masami plans to have sex with his own possible future daughter who hasn't even been born yet. Yukiha is perfectly okay with this.
Porn with Plot: Well if you can call it a plot.
Reasonable Authority Figure: The teacher Takamine is the only one who shows concern when both Yukiha and Aida disappeared from school.
Sex Face Turn: Inverted, Yukiha becomes corrupted and evil after she becomes Masami's sex slave.
Sex God:Masami is an ugly bastard and a vile rapist, but it can't be denied he is great at sex. When Yukiha become his sex slave willingly, they have sex until morning, at which point Yukiha is completely worn out. She describes sex with him as heaven.
Sex Slave: Yukiha was originally this due to blackmail, but as she becomes more slutty and corrupted, she becomes this of her own free will.
Slipping a Mickey: How Masami raped Yukiha to begin with.
Slut Shaming: The sex tape made by Masami gets leaked out causing Yukiha to be expelled from school and disowned by her parents. Considering she's okay with her child being raped or aborted and aided in her teacher being raped, she deserves it.
Speed Sex: Aida, and it drove Yukiha into the arms of her own rapist.
Stay in the Kitchen: At the end of episode/chapter 4, Yukiha is seen cooking dinner for her and Masami.
Teeny Weenie: Yukiha mocks Aida by saying he has the dick of a child. However this may be because Masami is much bigger. Nevertheless, this breaks Aida's heart.
Took a Level in Jerkass: Yukiha after she becomes Masami's sex slave willingly. She's implied to be perfectly okay with her possible future daughter being raped, or her possible son being aborted. She also mocked Aida's poor performance while he listens. In Chapter 5, she even helps Masami with raping Takamine, becoming just as evil as he is.
Ungrateful Bastard: Masami's reaction to Yukiha saving him from being fired is to rape her.
Victim Falls For Rapist: It's not so much Yuikiha falls in love with Masami, but she becomes a slut that just wants him for his sexual prowess.