Yoshiko Koizumi, a classmate of Shota Ohara, lives with her family and shares her home with U-ko, a ghost from the Obake world, forging a unique coexistence that bridges human and supernatural realms. Known affectionately as "Yotchan" at school, she actively engages in campus life, notably rallying support for Shota during his uphill battle to earn a spot on the baseball team. Her encouragement extends to Q-Taro, whose earnest but bumbling efforts to contribute—despite minimal grasp of the sport—add levity to tense moments.

Loyal and quick to laugh, Yoshiko balances steadfast support for her peers with playful reactions to Q-Taro’s mishaps, underscoring the narrative’s humor. While her cohabitation with U-ko anchors a key story dynamic, the nature of their bond remains rooted in shared space rather than elaborated interactions. Her presence consistently reinforces group camaraderie, though her personal history and family life remain unexplored, focusing instead on her role in episodic challenges and her quiet stewardship of U-ko’s place in the human world.