Sana Hayami is Yoshiharu Hayami's older sister, residing with their mother and younger brother. She maintains a consistently dismissive and unfriendly demeanor towards Yoshiharu, frequently appearing annoyed by his presence and upholding emotional distance within their household. Her physical traits include dark blue hair and brown eyes.

Sana's pivotal decision to move away from home prompts Yoshiharu to confess his intense feelings for her, a revelation that shocks Sana and underscores her initial lack of reciprocation and discomfort with his advances. Her brother's subsequent forced advances occur in multiple settings, including her bedroom and a staircase, where she resists and pleads for him to stop.

Despite the initial resistance and violation, Sana develops conflicted emotions towards Yoshiharu during these encounters. This shift involves a gradual, conflicted reciprocation of his intense emotions and physical attentions, resulting in an ongoing complex relationship between the siblings defined by taboo desires. The dynamics within their family home and the consequences of their actions form the core of her character development across the narrative.