Kōko Matsumoto is a supporting character in the anime series Watashi ni Tenshi ga Maiorita! and its theatrical film Watashi ni Tenshi ga Maiorita! Precious Friends. She is introduced as a young woman who attended the same high school as Miyako Hoshino and was a fellow member of their school's sewing club. While Miyako barely remembers her from that time, Kōko has harbored an intense and obsessive fixation on Miyako ever since, to the point of following her every move and memorizing personal details about her life. Her personality is defined by this deep, one-sided devotion. She is cheerful, persistent, and unabashed in her adoration, but her behavior can come across as unsettling to others because of its intensity. She considers herself Miyako's friend despite Miyako’s near-total lack of awareness of her, and she often tries to insert herself into Miyako's daily life. Her primary motivation is to be acknowledged by and become closer to Miyako, whom she admires above all else. In the story, Kōko serves as a supporting figure whose relentless pursuit of Miyako creates comedic contrast and highlights the dynamics between characters. Her key relationship is with Miyako, but she also has a younger sister named Yūna Matsumoto. Over the course of the series, Kōko shows little outward development because her fixation remains constant, though at times her actions reveal a softer, more earnest side beneath the obsessive exterior. She does not possess any supernatural or combat abilities, but she demonstrates a high level of skill in sewing and costume making, a hobby she adopted in part to emulate Miyako. Her persistence, attention to detail, and willingness to go to great lengths for the object of her affection are her most notable traits.