When your sister is kidnapped and brainwashed in order to save the brother, that makes the brother terrible for failing her on more than one occasion. And as it turned out saving her was not only possible but the best outcome.
But he did save her, and will spend the rest of their lives dicking the bad out of her, one tender night at a time
Besides, this is the only happy (and I use that term very loosely, given what happens to her prior to you rescuing her and taking her away) end for Lise.
>Used goods because she wanted to protect her brother from STASI
>Deserves anything but love after the shit she's gone through
Axxman, please leave
>fucks his sister every day
>likes tsundere, so is a man of taste
>actually goes determinedly for the imouto ending instead of some vague shit
>denies all the other girls for imouto
It really can't be beat, he's a good brother throughout the whole route, and next comes recovery, healing, and
As long as he protects this smile for the rest of his life, his past retardation can be forgiven