Isayama Yomi is the sisterly figure for Tsuchimiya Kagura. She is good spirited and optimistic in the flashback of the anime. She lost her parents at a young age to spectres, and was taken in by Isayama Naraku, then head of the Isayama family. Yomi grew to love and respect her foster-father, and polished her skills to repay him for his kindness. Her efforts led to her inheritance of the priced Isayama heirloom, the sword Shishio, which held the spiritual beast Ranguren in it.

A skilled swordmaster, she later became the very thing she fought to destroy.