Otsu Tsurugaya fulfills the maid role for the Otogi Bank club at Otogi High School. She is defined by an intense, overwhelming compulsion to repay every favor she receives, no matter how small. This behavior originates from a traumatic childhood event: a young boy pushed her from the path of an oncoming bus, sacrificing his own life. His death left her unable to thank him or repay his ultimate kindness, instilling a deep-seated fear of ever being incapable of reciprocating. Consequently, she obsessively settles perceived debts immediately, often to an excessive degree.

Throughout the series, other Otogi Bank members, including Ryoko Okami and Ryoshi Morino, actively support her in confronting and managing this psychological burden. Their intervention aids her gradual recognition of her obsession's unhealthy nature and her efforts to moderate the behavior, indicating personal growth.

Her Otogi Bank duties center on maid tasks, aligning with her preference as she refuses to cosplay in any other attire. Physically, she possesses long brown hair extending past her hips and brown eyes. She maintains friendly relationships with fellow club members Alice Kiriki, Liszt Kiriki, Otohime Ryugu, Ringo Akai, Majolica le Fay, Ryouko Ookami, Tarou Urashima, and Ryoushi Morino.

The character draws direct inspiration from the crane in the Japanese folktale "Tsuru no Ongaeshi" (The Crane's Return of a Favor), mirroring its core themes of gratitude and reciprocity. This cultural reference underpins her narrative function and personal struggle.