what if he ate his twin in the womb xD

You say that with a smile and laugh, but that is pretty much what a vestigial twin is. A twin that was "eaten" (or more appropriately absorbed) by the other twin. I have an aunt that had one of those....

oh my god no stop please T_T That makes his whole ability a lot less fluffy. Doesnt that mean his ability would allow him to identify cannibals? XD And couldn't that mean that the seme, who's a rainbow, is like a high-level cannibal? Wow, I need to go wash out my brain