[[Incest]]uous romantic or sexual relationships between [[twins]].

Common examples include [[kagamine_rin|Rin]] and [[kagamine_len|Len]] from [[Vocaloid]], [[Xia Yu Lan]] and [[Xia Yu Fan]] from [[Full Metal Panic!]], and [[Hisui (tsukihime)|]] and [[Kohaku (tsukihime)|]] from [[Tsukihime]].