His answer was to continue struggling to save people, naive indeed imo but i just see it as a different way of life, a contrast to Hajime, which is right is personal preference.
Hajime always values his loved ones over all else, while Kouki won't just immediately give up on others, i think the previous arc made it clear he does value his love ones over everyone else, he just doesn't want to have to make that choice hence he continues struggling trying to save everyone.
"He keeps trying to find the option where even his foes can be happy which is honestly just as bad as his thought process in Tortus and the guy still can't kill humans he's still wavering in his convictions just not as much as he used to be. "
He wants everyone to be happy sure, but not being able to kill is wrong, last arc with him proved that, he killed like thousands of ppl, if you are referring to him vomiting upon learning he was killing ppl against Mother, what did you expect from a normal person? You literally found out every single one of the robots you destroyed where actually ppl, that will mess with a lot of ppl. Hajime isn't normal, his mind set shouldn't apply to others, and that's what makes him basically the best part of Arifureta, that he is different, that said i think saying Kouki can't kill ppl is wrong, he will kill, if it's to protect those he cares for.
Maybe there are more, but what we known is only 9 exist, nothing supports any more. An infinite multiverse would be cool though.
My prediction is this final boss is Low Multivesal, a threat to the 9 worlds which are probably universes since they have their own flow of time. That's just wishful thinking though.