Even with their obvious conflict of interests, they both recognize that if it wasn't for Takeru, they could have been close friends. She even acknowledges that she doesn't have the same appeal the other girls have, as her life revolves so heavily around Takeru that she feels she may be too one-note for him.Дespite being love rivals with Mitsurugi Meiya, she has an amiable relationship with her.

She often wonders if she acted as too much of a childhood friend to him, instead of asserting herself as a woman. She keeps a personal diary, where her daily life, and most importantly, her memories and feelings for Takeru are written.ДЄs time goes on, she soon realizes that she has to take action to get Takeru to notice her as a woman, and that her relationship with him can't stay the same forever. Her room is right across from Takeru's, with only a small space separating their windows, and they often have short conversations before going to bed. She is a hard worker and always tries her best in school, despite not being particularly smart. She is a bit of an airhead and has a bubbly personality, which leads to Takeru often teasing her under various circumstances, which in turn leads to light-hearted fights that tend to attract the attention of their classmates. Another portion of her childhood was when she often played with Takeru in the 'Pee Park.' She continues to live a normal everyday life with Takeru, expecting to continue living those carefree days forever, until one morning, when she goes to wake Takeru up after his parents leave for an extended vacation and finds a mysterious woman in his bed. She cherishes the various memories that Takeru has given to her, as well as things like the 'Santa Rabbit' he gave to her one Christmas. For her, she can barely imagine what life without Takeru would be. Sumika is the childhood best friend of Shirogane Takeru, who has lived next door to him nearly her entire life.

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