|Affiliation||Gotei 13, Soul Society|
|Previous Position||Seated Officer in the 1st Division|
|Previous Division||1st Division|
|Previous Partner||Genryūsai Shigekuni Yamamoto|
|Relatives||Shūsuke Amagai (Son)|
Similar to his son, Shin'etsu keeps his dark brown hair in a messy fashion, though he has a small beard. As a seated member, he wore the standard Shinigami uniform, albeit it was tattered.
When the Kasumiōji Clan began manufacturing the Bakkōtō, the Central 46 denied Captain Genryūsai Shigekuni Yamamoto's request to investigate the compound. Nonetheless, Shin'etsu offered to sneak in anyway. While there, Gyōkaku Kumoi found him and forced a Bakkōtō on him. Kumoi then ordered for him to kill the person that sent him. He returns to Yamamoto, but his captain unleashes his Shikai to defend himself. Despite his hesitation, he kills Shin'etsu. Shūsuke finds his dying body and hears his father's last words, "Beware the Bakkōtō".
Powers & Abilties
Despite having a Zanpakutō, it was never seen released, due to his capture and later on death.
Upon being captured by Kumoi, he was forcibly given an experimental Bakkōtō. It has two curved extensions on both ends of the blade that take the appearance of a hook. Its powers, if any, are unknown.