Kaiwan

is one of the four guardians that guard the entrance to the Seireitei. He is the guardian of the Blue Stream Gate (Eastern Gate).

Soul Society arc
Sōsuke Aizen hypnotizes him and two other gate guardians and used them to cause trouble for Ichigo Kurosaki and his friends. But he is stopped by Jidanbō Ikkanzaka and Kūkaku Shiba.