Tsumugi is voiced by Dorothy Fahn

Tsumugi is a tall young woman with long, knee length, cerulean hair which starts smooth and becomes wavy the lower it goes. Her eyes are soft teal and round. She wears rimless glasses with white temples.

Tsumugi is an honors type student who speaks in a docile and gentle way, but she becomes very passionate when she talks about her favorite series or cosplays, having a habit of slipping infamous quotes from various sources into the conversation. Being a self-proclaimed introvert, she also tends to ignore people while she's in her thoughts, no matter how many times they try talking to her, and appears rather distant at times. She tends to call herself and everything that she has done "plain," as she believes that among all of the students, she is the one who has the plainist appearance and personality. She uses the word repeatedly and sometimes appears even offended if someone else tries to argue that she isn't plain. She understands that some people might not recognize her as the Ultimate Cosplayer since her plain appearance conceals her talent.

While Tsumugi is the Ultimate Cosplayer, she only enjoys making costumes, not wearing them, as she is not really fond of people looking at her. However, she hates using cosplayers who care more about standing out than love of the characters, so she wears her own costumes as well but with love.[7] She deeply loves cosplaying as she states that cosplaying is an expression of love. She has deep respect for fictional characters and gets very offended if they are disrespected.