Tsubame Ōse, a 15-year-old first-year high school student from Shizuoka Prefecture, was born on June 7, 2000, and stands at 157 centimeters with reddish-brown hair. Her devotion to the musical group FreyMENOW drove her to Tokyo for their concert, where she encountered the supernatural Phenomenon and joined the Trinary team.

In middle school, she faced repeated hospitalizations from a hereditary illness marked by debilitating headaches, inherited from her mother. Two years before her recruitment, a life-saving brain surgery ended her near-death struggles, with FreyMENOW’s music anchoring her emotional strength throughout her recovery.

Persistent worries about her mother’s ongoing hospitalization weighed on her before the concert. Hesitant to attend due to her mother’s declining health, she ultimately chose to go after her father’s reassurance.

In combat, she wields bare-handed techniques, her movements accentuated by her signature red color. Designated as the "Saint" within the narrative’s framework, she bears a mission to reshape a bleak reality into an idealized society under guidance from an unnamed group.