I feel that the ending wasn't really happy at all, it left me even more sad for Punpun... He wasn't brave enough to kill himself and to go with Aiko and instead forced himself to believe he was having a normal and happy life... also what happened between Shimizu and Seki really felt so realistic that it just hurts, like... all the time together and memories for what? Also (lol sorry for the long text im quite amused) poor Aiko she really didn't deserved what happened to her...
SPOILERS
I feel that the ending wasn't really happy at all, it left me even more sad for Punpun... He wasn't brave enough to kill himself and to go with Aiko and instead forced himself to believe he was having a normal and happy life... also what happened between Shimizu and Seki really felt so realistic that it just hurts, like... all the time together and memories for what? Also (lol sorry for the long text im quite amused) poor Aiko she really didn't deserved what happened to her...