I really vibe with the idea that BSD Dazai is asexual with low libido. Maybe it's me projecting my own asexuality onto him, but I think it'd be an interesting concept to explore.
Countless times in media, I've seen the whole idea that "love" - typically relating to romance or sex - is what makes us human. Society itself seems to revolve around the topic. Sometimes this leads to people on the aro or ace spectrum feeling broken or inhuman, which is incredibly depressing.
I can see Dazai experiencing a lack of sexual attraction, which further worsens how disconnected he feels from others.
Along those lines, I also think he'd have low libido, perhaps partially due to the depression. I defo think this man has cracked someone before tho lmao. I bet he tried sex to feel something, but ended up feeling empty afterwards.
Anyway, asexual Dazai is an underrated headcanon. I'll see myself out.