Aki Tezuka is Erika Shinohara's classmate and friend, initially forming a social trio with Erika and Marin Tachibana. Aki greets Erika's claims of a boyfriend with skepticism, actively testing their validity alongside Marin. This pressure contributes to Erika fabricating a relationship with Kyouya Sata. Aki demonstrates perceptiveness, as she and Marin discern inconsistencies in Erika and Kyouya's behavior, suspecting the relationship might be false. When Erika confesses the fabrication, Aki accepts the truth readily and transitions into a supportive role, expressing genuine happiness for Erika and interest in her evolving relationship with Kyouya.

Aki's personal storyline centers on her romantic relationship with her older boyfriend, Hajime Mukai. This relationship faces a major challenge when Mukai plans to move overseas for work, intending to go to England according to some sources or Italy according to others. The impending separation causes Aki significant emotional distress. Kyouya and Erika, drawing on their experiences, offer support; Kyouya directly advises Mukai he would either take his partner or stay, implicitly urging him to preserve the relationship. Aki's conflict over Mukai's relocation serves as a thematic precursor to a later, similar challenge faced by Erika and Kyouya regarding potential separation due to educational opportunities, highlighting common relationship hurdles.

Visually, Aki has red hair, positioning her as the "redhead" within the visual trio alongside blonde Marin and brunette Erika. Her name, "Aki" (愛姫), combines the characters for "love, affection" (愛) and "princess" (姫).