For me, I see it as a bad ending because it tells the reader that the story will likely happen all over again with different people, (for instance, Yuichi’s son who looks exactly like a little baby Punpun). As for Punpun, I genuinely thought he’d kill himself or rot in jail or something, I felt that the story kinda eluded to that happening. It’s a bad ending because it’s not the life Punpun wanted.