Daiki Aizawa is the younger brother of Natsumi Aizawa, one of the four main protagonists of Natsuiro Kiseki. He lives with his family in Shimoda and is a regular presence in the Aizawa household. Daiki is of elementary or middle school age and has short brown hair. His personality is stubborn and pragmatic, a trait he shares with his older sister. He is skeptical of supernatural claims and does not believe in the magical rock that Natsumi and her friends discover. This skepticism places him in contrast with his friend Yusuke Kimura, who becomes convinced that the girls can fly after witnessing them. Daiki often spends his free time playing video games at home or hanging out with his friends Yusuke and another boy named Keita. Despite his stubbornness, he cares about his friendships. In one instance, he argues with Yusuke when Yusuke insists on his witch theory, but Daiki eventually reconciles with him after Natsumi pushes him to do so. As a sibling, Daiki is a source of responsibility for Natsumi. When their mother is away, Natsumi is tasked with looking after Daiki in addition to her tennis practice and studies. This reveals his role as a typical younger brother who can be both a handful and a motivating factor for his sister. He does not possess any supernatural abilities and his role in the story is primarily as a supporting family member and friend to Yusuke, providing mundane interactions that contrast with the magical events. Daiki does not undergo major personal development over the course of the series, but his relationships with Natsumi and Yusuke are touched upon, showing his capacity for reconciliation and his loyalty to those close to him.