Sumika is Takeru's childhood friend. She has been his neighbor since they were little. Their rooms are right across from each other, with only a small space separating their windows, and they often have short conversations before going to bed. Sumika is madly in love with Takeru. However, her bubbly personality and rather idiotic demeanor prevents him from realizing her true feelings. She has a signature attack that she has dubbed "Drill Milky Punch."
Sumika's existence in the Unlimited universe is initially of top concern to Takeru. However, he is later told that there are no records of her ever existing and eventually forgets about her.