Yu is a benevolent tsukumogami dwelling within the Nagatsuki household, one of six ancient spirits inhabiting aged objects who live under Botan Nagatsuki's protection. This group forms a close-knit family unit, with Yu as an integral part of their dynamic.

She embodies the household's demonstration of peaceful coexistence between humans and spirits, serving as a direct counterpoint to the antagonistic views of the Saenome clan. While her specific object origin remains undefined in the documented narrative, Yu stands as a steadfast member of the collective safeguarding Botan and maintaining harmony in their unique shared life.

Throughout the series' events, Yu participates in the household's daily life as a supportive presence among the Nagatsuki tsukumogami. Her character actively embodies the potential for mutual understanding between humans and tsukumogami, challenging deep-seated prejudices against spirits.