Rooted in Japanese folklore, Yui’s origins trace to the Lowly Realm, where she once lived as a crane. Injured by a hunter’s trap, she was rescued by Kinta, who mended her leg. Overwhelmed by gratitude, she grew deeply attached to him and yearned to become human. The Visitors—twin goddesses—granted her wish on one condition: she must never disclose her true identity. Her name, meaning "to connect," embodies her dual purpose: weaving garments and intertwining destinies.

After fleeing enslavement with Kinta, Myrthe, Tauemon, and Kaimaru, she settled on Hinoe Island in the Lofty Realm. Her weaving, essential to the group’s survival, produced armor and clothing from gathered materials. Yet she barred others from witnessing her craft, guarding the secret of her avian past. When her crane form was accidentally exposed, she reverted permanently until The Visitors imposed a new pact: obey Kinta unconditionally, even if it shattered her hopes for peace on the island.

Central to her journey is her bond with Kinta. What began as indebtedness gradually shifted into loyalty and quiet affection. His decision to return to the Lowly Realm forced her to confront her own desires, culminating in a choice to stay on Hinoe Island—a testament to her growth in balancing duty and authentic bonds.

Her interactions expose further depth: she shields Kaimaru, deciphering his animalistic speech despite frustrations; collaborates pragmatically with Sakuna on survival needs; shares a familial warmth with Myrthe and Tauemon; and offers wary reverence to the divine leader Lady Kamuhitsuki.

Echoing the folktale *Tsuru no Ongaeshi*, her story weaves gratitude and sacrifice, positioning her as a bridge between mortal and divine. Her transformation between crane and human forms mirrors this duality, while her evolution from obligation to chosen loyalty unfolds through her craftsmanship and relationships.