[ flat tilts his head to the side, giving rin a look that clearly says that he doesn't really see where she's coming from. to him, the answer is much simpler. ]

I don't see why the world would need to prove that it's worth saving. If you want to save the world, then you should do it because you want to, not because it's worthy of it. [ a pause. ] I mean, if you want to curse the world instead, then I also think that's fine. Just as long as you're doing what you want and you don't regret it later on.

[ in that sense, flat is also someone who moves forward. or, perhaps, it's best to say that he moves as if the world were nothing but an empty expanse, rendering any sort of direction useless. so long as he's moving, it's good enough for him. ]

There's no value in either option. That's why both options are priceless!