Koishi Herikawa is a supporting character in the anime series Please Teacher. She is a high school student and a close friend of the protagonist Kei Kusanagi, belonging to the tight‑knit group of classmates that surrounds him. Koishi is portrayed as a shy, gentle, and kind‑hearted girl with a generally cheerful disposition. However, she often struggles with hesitation when it comes to matters of the heart, and she is most visibly upset only in situations that involve Kei. Her primary motivation throughout the story is her romantic feelings for Kei, which she finds difficult to express openly. This unspoken affection leads to quiet pining and a tendency to hold back, even when encouraged by others. Her friend Ichigo Morino sometimes grows frustrated with Koishi’s reluctance to act on her emotions, as it ultimately means she waits too long to confess. By the time Koishi musters the courage to reveal her true feelings, Kei has already fallen deeply in love with the alien teacher Mizuho Kazami. Despite this heartache, Koishi remains a supportive friend and does not let her personal disappointment disrupt the group’s harmony. Later in the story, her character experiences development as she gradually discovers affection for one of her own teachers, Masaomi Yamada, indicating her ability to move past her earlier attachment and find new direction. Koishi is also artistically inclined; she has a passion for drawing and dreams of becoming a professional manga artist. Her talent and dedication to art are recognized by her peers and teachers, and she often spends her free time sketching. In the overall narrative, Koishi serves as a reminder of the quiet, everyday emotions that linger beneath the surface of the main romantic plot, and her journey reflects the themes of unrequited love, patience, and personal growth present in the series. She appears in both Please Teacher and its spin‑off Please Twins.