Narushima Ai

She used to live next door to Kento when he was living in an apartment complex (he lived there until he graduated from high school). She was also a swimmer in school and taught Kento how to swim for the first time.

When Kento was 12 years old, they were separated by Ai's marriage. She married for the sake of her dying father, it is difficult to say that she married the person she truly loves. However, she has spent the last 10 years of her life without letting her husband and people around her realize this.