HELLO ANONNIE! and hmm i'd actually recommend u read the manga. while i do think that the anime is a good adaptation for the most part, they make some omissions and changes that pretty drastically shift characterization imo, especially where dazai is concerned.

and in general, i do think that bsd is best experienced as a manga, but that's just me! you can always watch a couple episodes of the anime first and then read the manga and decide what you'd rather do from there hehe.