Man, imagine if Battler really had somehow returned to Ange after beating Beato. She'd be the biggest brocon in the world, never letting him out of sight. He wouldn't even get to go to the bathroom by himself, since she'd refuse to leave him alone. She'd just sit on the bath stool and watch him pooping. He'd have to get over the performance anxiety of having someone watch him shit pretty quickly because she'd never let him do it without her staring straight into his eyes the entire time.
He could kiss goodbye to private masturbation time too. She'd watch him in his sleep, waiting until he drifted off and then, and only then would she allow herself to go to sleep, holding him tightly to make sure no witches can come in the night and take him away. He'd get so pent-up, never being able to get off, to meet any girls for a quickie, to do anything involving his dick because his sister would never allow him to do so without her in the room as well.
It'd grate on him eventually, being stuck, unable to masturbate. And over time, Ange would start looking more and more like the succulent pig she is, the easiest method to release his urges. He'd have never even entertained the idea originally, but after months, years of enduring her constant spectatorship, his very moral compass would have been affected.
And yet, after just the wrong words said by Ange one day, after he got so irritated he gave in to his urges and pushed her down, as he stripped her down and used her like the disgusting onahole she was born to be, she'd never complain. No, she would be happy. Happy her brother finally saw her as a sexual object, happy he finally did what she'd been waiting for, happy they could finally be together. Isn't that disgusting? Watching her brother for years, giving him no privacy, under the guise of expecting him to disappear at any moment, while in reality wanting him to eventually crack and break the bonds of blood so she could finally fulfill her brocon fantasies? What a disgusting beast.
Ah, but it would probably be the best experience Battler had ever had, having a girl dedicated to you, to squeezing you dry every time you want it, so overwhelmingly great in her love. After going for so long without that sort of affection from another, it would feel like the oasis in the middle of the desert. Ange would become the perfect onahole, the perfect woman for him, entirely because he couldn't remember any better woman at this point, a woman who didn't watch him piss everyday, who would leave him alone for even a few minutes, who would let him breathe without making sure that air wasn't poisoned too. What a sick, sick girl, to break her brother so thoroughly.
It's a good thing their family are dead, lost to that explosion he'd read up about once he'd returned to the land of the living, for they surely would look down upon their relationship. Battler wouldn't know, of course, that they never could have looked down upon him in this situation. No, the entirety of the blame was squarely on Ange, for having done such a thing to him. He would never know that though, and so the shadow of doubt would never be lifted from his shoulders, the heavy weight of responsibility crushing him, reminding him that he continued to use his little sister, his cute little sister that he'd left for so long, that he'd returned to so she would never have to be sad again, and perhaps in a way he was doing just that by giving her the daily allowance of cum every morning, noon and night.
It still would feel wrong though. And yet, so right.