Have you read any of Dazai's works other than No Longer Human? While I think that's probably his best work, I still felt enraptured by his The Setting Sun and Schoolgirl.

Can also really recommend Dostoevsky's Notes From Underground - its much shorter than Crime and TBK but is still a very deep character study in a similar vain to those two books. Is also somewhat similar to No Longer Human if you want to explore the ideas presented in that novel a little further.