Adachi Atsuka is the mother of Adachi Sakura, resembling an older version of her daughter. Her personality contrasts sharply with Sakura's introversion; Atsuka is more social but exhibits a blunt, often confrontational demeanor. She speaks her mind directly, sometimes appearing dismissive or tactless, as when she told Shimamura she disliked her due to youth and attention-seeking, framing it ambiguously as a joke.

Atsuka's relationship with Sakura is emotionally distant. Though providing necessities like meals, she was emotionally neglectful. This dynamic began when Sakura was four or five; after Sakura's indecisiveness, Atsuka largely stopped trying to understand her. She spoke poorly of Sakura to others, further straining their bond. Their frigid home life contributed to Sakura's reserved nature and emotional struggles. Atsuka lives with Sakura's father but is unmarried, implying Sakura was born out of wedlock.

Key interactions occur across the series. In Volume 2, Atsuka meets Shimamura at a sports gym and engages in a 'contest,' revealing her confrontational side. Shimamura later avoids suggesting study sessions at Sakura's house to evade her. By Volume 9, Atsuka encounters Shimamura's mother, who invites her to their home for Christmas. In Volume 10, during a flash-forward, Atsuka watches Sakura move out permanently. She silently acknowledges the unlikelihood of mending their relationship and offers a tacit wish of luck. Post-move, they have no further contact.

Atsuka attended the same sports gym where she met Shimamura. Despite their estrangement, she does not dislike Sakura and fulfilled material needs while neglecting emotional ones.