Tomari is Hazumu's childhood friend who has been with Hazumu for a long time, and most importantly protected him often from bullies. In direct contrast to Hazumu, her most obvious quality is that she is a tomboy which is shown through her actions and lack of interest in traditionally feminine things such as clothing or shopping. Indeed, Tomari's friends of both genders consider her very masculine which often causes Tomari to get angry at such comments. Additionally, she is a member of the Track and Field Club and enjoys physical activities.

Before Hazumu's change, she shows some latent interest in Hazumu and is at first just as shocked as everyone else when he is transformed into a girl. Tomari has always put a lot of effort into supporting Hazumu and defending him whenever he is in despair. Though Hazumu has always been grateful for Tomari's support, at times Tomari later seems to be jealous that Hazumu hangs around with Yasuna a lot more after Hazumu's sex change. Eventually, Tomari seems to develop romantic feelings of her own for the new Hazumu.