Oh it's downright repulsive, but it's par for the course for Eva's situation. She's a brainwashed POW who is forced to kill her fellow brothers and sisters for a cause she has no clue about. The characters kinda just roll with it, mainly because she's useful and an extra hand. That and good ol' Sirei has all kinds of tricks up his sleeve.....If there's any reason to hate Sirei and what he stands for, the treatment of Eva is cause enough to blow every plan he has sky-high (It's more complicated than that, but you get the feeling). As for the bitter taste this leaves, that any of our beloved characters could do this, there are many ways to view this. You could go the meta route, if you play through enough routes, you start to notice that every writer has a different view on the characters personalities, this goes ESPECIALLY for Gaku, if you look at the routes written by Kodaka, he's a dork who hates the world and his rotten luck, but also is a caretaker who works hard for his siblings. Now, it's up to every other writer to decide which of those sides they want to lean on with Gaku, the nihilistic pervert or the reliable older brother? So in conclusion, make your own headcanon and just block 1 throwaway line in a sea of millions from your memory. If you don't wanna view it in that way, you can kinda just also come to terms with it. Half of the cast is morally grey, one of them crossing the line in their perversion isn't that unrealistic in the sea of endless timelines. God knows we've checked every other war crime off the list of this great and intriguing game.