Ayumi began as a pet turtle adopted by Gorō Mutsumi on November 20, 1984. During winter, Gorō observed her attempting to hibernate and dug a shelter in a park beside a ginkgo tree. A girl also named Ayumi assisted him, sparking their friendship. Come spring, park demolition led to the ginkgo tree’s destruction, crushing Ayumi. Gorō and the girl buried her.

Reincarnated as a Senior-ranked Guardian Angel, Ayumi has gray hair and eyes, wearing a green beret symbolizing her turtle shell. Her death left her with achluophobia and claustrophobia. She displays a deliberate, thoughtful nature, often seeming slow due to weighing future consequences, contrasting her frequent arguments with Mika in a tortoise-and-hare dynamic.

In the angel hierarchy, her color is black, and she serves as bride to Shin, the Black Turtle. She holds strong reciprocal feelings for Shin, standing out as the most emotionally responsive among angels abducted by the Four Saint Beasts. When Shin saved her from a collapsing warehouse at great personal risk, her devotion became clear, though she acts shy around him and struggles to voice her emotions. Once, she invited him to the Full Moon Festival, but his poor health forced a decline, requiring Goh’s consolation.

Her growth includes confronting fears to protect Gorō and deepening her connection with Shin. Recognized as a sisterly figure among angels, she contributes to their shared mission despite personal struggles.