Tatsuya Yuutenji belongs to the wealthy Yuutenji family. He attends the celebration after Sara Bihada wins the World Bihada Challenge (WBC), taking particular interest in Sara. Later, he facilitates Saki Bihada's flight from her family by providing transport after she steals the Bihada family treasure, Bihada Shichihouten.

Three years after Sara's WBC victory, the Yuutenji family acquires the Bihada family's dilapidated mansion through financial means. Saki, now allied with Tatsuya, asserts ownership of the property and uses it to torment her sister Sara. Tatsuya then marries Saki, cementing her integration into the Yuutenji family and enabling her complete break from the Bihada lineage. This marriage elevates Saki's status and positions her as head of the cosmetic company U10G, where Tatsuya is also involved.

Tatsuya displays a calculated, opportunistic stance toward the Bihada sisters' rivalry. He observes their escalating conflicts with detached amusement, such as laughing while remotely viewing Saki's aggressive pursuit of Sara involving a vehicular chase and grenade launcher. He expresses no allegiance to either sister, prioritizing the acquisition of the strongest individual for his interests. His surveillance capability is shown through U10G's use of satellite technology to monitor Sara's beauty regimen training.

His influence extends corporately through U10G, where his presence and authority intersect with Saki's management. Sara directly blames him for Saki's continued hostility toward their family, perceiving him as the instigator of her sister's psychological shift.