There were 2 siblings (maybe?). A boy and a girl they get separated by some adults (probably orphans sold out to different people). The Boy gets sent to this cult like place and get castrated. Fast forward, he's all grown up, but looks completely feminine with long black hair and has huge breast and kinda ditzy and spacy probably. I remember he was performing naked (except wearing a hat and a long cape) and singing in a Opera House. Also remember that he somehow made a blonde hair female friend and that friend got killed or something by a monster disguised as a man.

it sounds really similar to a case from God Child (chs 29-33) but there are some differences to what u described

The manga in looking for has more of a modern realism style similar to AirGear and DeathNote. However, I've read God Child before. So nostalgic.

I FOUND IT! Godeath - Megami No Ketsumyaku