Hatsuho Sasahara is Yu Ominae's classmate and the older twin sister of Kagaho Sasahara. Drawn into the "Mask of Palenque" incident when the artifact affects her father and younger sister, she travels to Mexico. There, she aids Yu in freeing Kagaho from the mask's control and rescuing their father from the entity Tezcatlipoca. This experience reveals Yu's dual life as a Spriggan agent to Hatsuho, Kagaho, and their teacher Suzuko Kawahara, making her one of the few surface world individuals privy to his covert activities.

Hatsuho possesses a vibrant and sociable personality. Esteemed as a dependable classmate, she exemplifies fierce loyalty to her family and friends, showcased by her determined efforts to protect Kagaho throughout the Palenque crisis. Proficient in karate, this skill reflects her active and resilient nature.