Sanae Yamishi appears in the anime adaptation of Nijuushi no Hitomi. She is one of the twelve first-grade students in Ooishi Hisako's class at the isolated Detached Classroom on Shoudoshima island during the 1928 school year. Initially characterized like her classmates, Sanae responds positively to Ooishi's cheerful teaching methods and bonds with her teacher during the early six-month narrative period.

Four years later, Sanae reunites with Ooishi Hisako as part of the same student cohort, now in fifth grade. This period depicts the increasing impact of Japan's militarization and societal shifts leading towards war. While specific personal experiences during the intervening years or detailed wartime actions are not elaborated, the broad consequences of the war period are established: half of Ooishi's original twelve students, including some of Sanae's classmates, were killed, maimed, or driven to despair during the conflict.

Sanae Yamishi's significant development occurs post-war. She becomes the student who follows Ooishi Hisako's path by becoming a teacher herself. Securing a position at the Detached Classroom, she takes the initiative to invite Ooishi, who retired due to wartime pressures and personal losses (including the death of her husband and youngest child), to return as a substitute teacher for a new generation. This act facilitates Ooishi's emotional return to the school and catalyzes a reunion involving Ooishi, her surviving sons, and the remaining original students.

Her role concludes within the narrative framework of facilitating remembrance and looking towards the future, symbolized by the survivors gathering at the Detached Classroom. Sanae Yamishi's arc embodies continuity and hope, directly linking Ooishi's pre-war idealism and teaching legacy to the post-war reconstruction era through her own profession and her effort to reconnect her former teacher with the school.