>asks her to marry him
>she says she'll reply tomorrow
>kill herself before then
No surprise it completely fucked up Kudo.
Felt kinda weird to me that she committed suicide, too. It was alluded to often enough, but she never came across like a person who'd do that to me. Even with the "I never want this to end" thing.
But I guess that was the point, since we see it from Kudo's perspective and he himself admits he didn't understand her at all, either.

They also managed to somehow make the ending both sad and happy.
She sounded like Reiko B on the very last line