I'm looking for hardcore guy chained up in the cellar type of yaoi. With a sadistic seme and yes I have read hoshi no yakata although that's hardcore but not really slave. I don't care about the ages of the uke and the seme. The smuttiest most yaoi you can think of!

I think Kinbaku by Zaria applies.

I so want this too! Been looking at Hoshi no yakata, but doesn't they sort of look like girls, at least in their faces... Still pretty hot though.

I don't have many suggestions though, but you might like these;
Aigan Shounen
Hakui no Shihaisha