Izumi Shimamura, maternal aunt to Natsumi Mizuki, is a 20-year-old Virgo born September 2, standing 165cm tall and weighing 32kg with blood type O. After losing her apartment due to unpaid rent—a consequence of prioritizing her manga career—she moves in with Natsumi. Driven by her aspiration to break into the manga industry, she often neglects responsibilities beyond her work.

Initially immature and self-centered, Izumi resents childcare duties and harbors a strong dislike for both babies and dogs, particularly Natsumi’s Irish Setter, Bobby. This cynophobia stems from childhood experiences shared with her mother, Koharu Shimamura, with whom she has a strained relationship marked by mutual resentment over past neglect and perceived favoritism toward Izumi’s older sister, Natsumi’s mother. Their reconciliation occurs when Izumi deliberately exposes Koharu to Bobby, sparking a confrontation that leads to understanding.

Forced to care for Mirai—Natsumi’s time-traveling future daughter—Izumi initially attempts to abandon the infant or pawn her off on others. Her evolution unfolds through pivotal moments: joining a search party for Natsumi and Mirai in bear-infested mountains and tearfully reuniting with them; urgently driving Natsumi to avert a predicted death during a school trip after a warning from future Natsumi; and fiercely protecting Mirai from a neighbor child, overriding Natsumi’s gentler approach.

Beneath her self-absorption lies loyalty. She enjoys Italian culture, especially food, and favors childlike overalls. Though clashing with Natsumi over household duties and Mirai’s care, she gradually grows fond of the infant and supports her niece. Her journey culminates in embracing her place within Natsumi’s makeshift family, balancing manga ambitions with newfound commitment.