Tsuina is Kotana Kifu's small pet mouse. As one of the reincarnated warriors, Kotana employs Tsuina to summon a Sacred Beast during combat, utilizing this ability as her primary means of engaging supernatural threats. Tsuina remains constantly at Kotana's side during these engagements. The specific nature and characteristics of the Sacred Beast summoned through Tsuina remain undefined, as do Tsuina's own origins, species background, or independent traits beyond serving as the conduit for Kotana's power.

Tsuina is frequently present during observed interactions between Kotana and Jutto Sego, the warrior of light, where a special yet unacknowledged connection exists between the two warriors. Tsuina, however, does not independently participate in or influence this dynamic.

In narrative execution, Tsuina serves exclusively as an extension of Kotana's capabilities. The character exhibits no personal evolution, explored background, or distinct personality traits across appearances. Tsuina's role is solely instrumental, enabling Kotana's summoning ability during confrontations.