Shin’etsu Kisaragi (如月 信越, Kisaragi Shin’etsu) was a Shinigami from the First Division and the father of Shūsuke Amagai.

When the Kasumiouji Clan began manufacturing the Bakkōtō, 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”.

(Source: Bleach Wiki)