I've only read the first 1-3 chapters when it first came out. 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 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 female friend and that friend got killed or something by a monster disguised as a man.

o̶t̶h̶e̶r̶ ̶m̶a̶n̶g̶a̶ ̶i̶s̶ ̶a̶ ̶y̶a̶o̶i̶ ̶o̶n̶e̶ ̶s̶h̶o̶t̶.̶ ̶S̶o̶m̶e̶o̶n̶e̶ ̶h̶a̶s̶ ̶t̶o̶l̶d̶ ̶m̶e̶ ̶a̶b̶o̶u̶t̶ ̶i̶t̶ ̶o̶n̶ ̶h̶e̶r̶e̶ ̶b̶u̶t̶ ̶I̶ ̶l̶o̶s̶t̶ ̶m̶y̶ ̶o̶r̶i̶g̶i̶n̶a̶l̶ ̶a̶c̶c̶o̶u̶n̶t̶.̶ ̶A̶n̶y̶w̶y̶a̶s̶ ̶i̶t̶'̶s̶ ̶a̶p̶p̶a̶r̶e̶n̶t̶l̶y̶ ̶a̶ ̶y̶a̶o̶i̶ ̶i̶n̶s̶p̶i̶r̶e̶d̶ ̶b̶y̶ ̶a̶ ̶p̶o̶p̶u̶l̶a̶r̶ ̶t̶h̶e̶a̶t̶r̶e̶ ̶p̶e̶r̶f̶o̶r̶m̶a̶n̶c̶e̶ ̶i̶n̶ ̶J̶a̶p̶a̶n̶.̶ ̶B̶o̶y̶ ̶g̶e̶t̶s̶ ̶d̶r̶u̶g̶g̶e̶d̶ ̶a̶n̶d̶ ̶r̶a̶p̶e̶d̶ ̶b̶y̶ ̶g̶l̶a̶s̶s̶e̶s̶ ̶f̶r̶i̶e̶n̶d̶ ̶t̶h̶e̶n̶ ̶i̶m̶p̶r̶i̶s̶o̶n̶e̶d̶ ̶i̶n̶ ̶t̶h̶e̶ ̶b̶a̶s̶e̶m̶e̶n̶t̶.̶ ̶

Found the yaoi. It's called D no Satsujinsha - Shoushitsu.