This is what i get after reading both manga and thr video fully sub
When they were little, otome and kazuki imouto used to compete eqch other for kazuki,
One day, at a park, he couldn't answer which one he loved more,
Otome ran away crying
Kazuki imouto beg him to stay by her side and let her be,
Kazuki ignore her and chase after otome,
It was revealed later that kazuki imouto got raped at the park by the same old man which is the leader of the gangbang gang that's currently raping otome,
Thn years pass, kazuki imouto was raped and blackmail without anyone's knowledge,
They finally at the age at every school manga for time is right for kazuki to confront and confess to otome, kazuki imouto seen this coming,
And nasty yandere incest love came to her, so before kazuki even got the chance to confess,
His imouto got the upper hand against the old man and his gang that been raping and blackmail her after all these years, and instead bring them to the law, she.counter blackmail them to work with her and sold.otome to them since she thought its its not fair only she's the only one being raped and all,then that the time when kazuki starting to received the disc,
In secret it was his sister that keep deliver the disc while the gang tape them raping otome slowly breaks her,
Kazuki didnt know that but felt betrayed,
So at the end of episode one, he ignored her when she tried to ask him nicely, and instead demand for explanation and the truth from otome, he kept quiet and the debauchery continues,
Following episode 2, the disc already reached volume 10, and Finally otome breaks and give in to them and said she doesnt care bout kazuki anymore,
Kazuki took his mini cpu or stereo and break the computer screen
He is confused and decided to take a walk, walking like a zombie, keep bump with walls and poles, in deep thought and regret, that he should had done something to prevent and helped otome, suddenly (in anime stumble upon his sister talking with the same old guys that met and rape and fuck otome and had a mindblown, the sister and the old man talk quite bit before they head to the park where kazuki imouto first time raped when she was little)
But in manga he stumble them at the park kissing, listening quietly, he finally knows that it was his sister orchestrated this whole scheme of otome being rape, delivering the dvd to him,
They both proceed to the nearest pub toilet to fuck, but the old man wasnt allowed to knocked her up, she threaten him and remind him what wilk happen if he creampied her and he came outside,
Out the toilet, kazuki had enough and his head is almost exploded with all of these sudden truth and and realization,
Suddenly someone hit him in the back and he's k.o
He woke up at home being tied up, seeing his own sister sit on him, confessing everything, and to make things worst, kazuki being stubborn and said its not too late to save otome and her
The sister kinda angry when he mentioned otome again and said that otome result came in and she's pregnant with one of the gangbang gang, she said everything was too late the moment he abandone her at the park to chase otome and he should just enjoy knocking her up since her pussy only reserved for beloved brother
Kazuki finally lost his mind and have sex with her, months later we could see kazuki still watching otome gangbang vid and she's gone into labour and gave birth after the disc is finish, his sister came into his room shown with big belly aswell, and said she's too gonna give birth soon, and with dead eye kazuki smiled and smooches with his sister while she mentioning otome gonna visit them soon, bringing the child and bam, its ended,
You can chose this to be the official end and stop watching the rest of the episode, at least kazuki got a little of happiness in this even tho its twisted and wrong
Or you can choose to keep watching for the extra that the manga have the same scenery aswell
This might be a spin off or alternate universe where kazukk sister failed in her uprise and counter blackmail the old man,
Otome still got raped and broke, but kazuki never received any dvd since his sister never deliver it, and without knowing the truth, he and otome end up together
He had a dream from his own self from another world and thought it was a nightmare
Kazuki woke up screaming, and otome run to comfort him, it has been years after they both got married, and had a little girl, and pregnant with a second child
He didnt tell otome what is the nightmare was and he was happy, for a moment, the next day, his wife went out shopping along with their daughter,
Suddenly he saw a dvd slip hidden in a tight spot near his pc, he was curious, and watched it, it was a scenery of his bedroom, during the time he was working, otome with her pregnant belly having gangbang sex with couple of old men
One of the man who was doing POV said the dna test finally came in and said the first little girl otome had as a child belong to him, otome happy admit and glad the child is his and said to make sure to sneak out next time from her husband to introduce her to her real father
As they proceed to have sex and argue who is the father of the second child, otome having the time of her life, apologizing to her husband while havinf a cock in her mouth, and getting creampied in her pregnant belly, and as they reach the endz they said to make sure otome work her husband hard as they promised to keep impregnated her over and over with a child that doesnt belong to kazuki,
Otome finally came home her daughter and we can see kazumi slip the dvd in his back pant pocket as similar ending from episode one happen, but this time instead being angry with otome and ignore her, he prayed so hard deep in his heart so let this be just a nightmare..
Because it is just too cruel.... For a reality
FIN
Sorry for the great wall of text, hope this will help you guys understand otomedori better