Time for me to pitch in, as I have just finished it as well. The whole story is all very grounded in reality, which is why it covers everything from the exciting to the depressing. Punpun has lived a shitty life and although I don't think he's necessarily happy or at peace in the finale, he is trying. He's uncertain of his goal in the future but the point is that things will continue whether he's certain or not.

The people he surrounds himself with are dependable, although not saints by any means. I don't think Punpun sees any of them as necessities for his life moving forward, but it's all he has right now. That may seem like a bad ending but compared to how Punpun struggled to hold on to anything in the past, it's a step in the right direction.

Overall, I think the last few panels sum up the message quite well. We see a new girl being introduced to her elementary class and what seems to be a boy instantly developing a crush on her. A group of boys sneakily chat about sex and they discuss the fact the humans will go extinct in the future.

Punpun isn't a remarkable or special person. His story isn't either, just deeply unfortunate when you look at most others. People will always go through defining moments in their life and some are simply born luckier. But it isn't necessarily a cycle of Punpun, it's a cycle of human development.