Isane
Kotetsu

Isane Kotetsu is the lieutenant of the 4th Division and later its captain, which makes her the person responsible for keeping the Gotei 13 alive through two wars. She is unusually tall, visibly nervous about most things, and has spent her career standing next to Retsu Unohana, who is the single most frightening person in Soul Society.

Her division does the work nobody else wants to acknowledge. The 4th are medics and they are treated as menial by the combat divisions, and Isane absorbs that without complaint while running triage under fire. Itegumo is her Zanpakutō, a blade that splits into three, and she is a competent fighter who almost never gets to be one because there is always someone bleeding out nearby.

She is at Sōkyoku Hill for Rukia Kuchiki's execution and openly upset by Yamamoto's promise to let the rescuers leave, which Unohana explains was said so Rukia could die at peace. That is the register Isane operates in: she notices the cruelty in the procedure and is told the procedure has reasons. When Unohana dies, the captaincy passes to her, and she takes a role she never asked for in the middle of an invasion.