Tōko Saionji is one of four female students encountering Kensuke Yamamichi on a camping trip. She attends the same school as the others and later joins the camping club formed with Yamamichi as their advisor. She owns a pet Welsh Corgi.

Initially shy and reserved, especially while changing, her demeanor changes drastically upon discovering Yamamichi attempting to observe her. Noticing the shape of his genitalia, she adopts a sexually dominant role, commanding him to obey like a dog. She stimulates him with her feet until he climaxes, then demands reciprocal oral stimulation until she achieves her own climax.

Later, during a group bath, she participates in an impromptu sexual encounter initiated by Aki Minami, engaging fully as others join. On another occasion, while searching near the campsite for her missing dog, she encounters Yamamichi and Minami together.

Her camping club involvement includes trips where the group depends on Yamamichi for transport and equipment setup. She participates in shared meals and communal camping experiences. During one camp, her temporary loss of the corgi leads her to discover two characters in a compromising situation during her search.