Mitsuki Utsunomiya, Kyōsuke Munakata's older sister and biological mother of Mira Munakata, became pregnant young and planned to raise the child with Kyōsuke. A Hollywood acting opportunity led her to transfer custody of Mira to Kyōsuke, who raised the boy as his son while Mitsuki achieved international fame. She later married a prominent film director; after his death, her stepson Takayuki Utsunomiya maintained her connection to that marriage.

Media rumors of an engagement between Mitsuki and Kyōsuke distressed Mira, who saw her as a threat to his relationship with Kyōsuke. These rumors were later exposed as Kyōsuke's strategy to provoke jealousy in Mira and reduce his shyness about their bond. Mitsuki actively supported marrying Kyōsuke, partly to elevate her celebrity status, with Takayuki assisting her while pursuing his own romantic interest in Mira.

The conflict peaked when Mira discovered adoption papers and briefly ran away, fearing Kyōsuke would marry Mitsuki. Kyōsuke found Mira, reassured him marriage to Mitsuki would not happen, and stabilized their relationship.