Shiori Daiichi was a close friend of Koharu Hayama, the dead mother of Akito and Natsumi. When she is first seen, it was believed by Natsumi and Akito, as well as Tsuyoshi and Sana, that he was the lover of Fuyuki. They attempt to make him seem as strange as possible to deter her, though she shows a high tolerance to their shenanigans.
As it turns out, she actually is Akito and Natsumi's godmother. Fuyuki reestablished contact with her in hopes of explaining Koharu before her death to Akito, who knows next to nothing about her. She explains she was a carefree and kindhearted, and loved all parts of her life.