Board Thread:Questions and Answers/@comment-6019258-20130325050319/@comment-5398287-20130325053434

We don't know what happened to Kugo in the past, as Kubo never really explained it beyond him being a Substitute Shinigami and betraying SS. The badge is never explained. However, he was able to perform Bankai because he replicated Ichigo's powers, aka his Getsuga Tensho and his ability to perform Bankai. Hope this helps somewhat.