Iko is a young child, a third-grade elementary school student, who resides in an old house in the seaside town of Tateyama. He lives with his four older brothers, and the household notably has no parents present, with his brothers explaining that their mother is working in Tokyo. Iko is described as being a bit eccentric, but he deeply loves his brothers, who take very good care of him.

Iko has brown hair that is cut short to ear-length and brown eyes. Physically, he has the appearance of a child of elementary school age. Some sources identify Iko as a girl, while others refer to him with male pronouns, but the description consistently emphasizes a youthful and childlike demeanor.

His primary role in the story is that of the youngest family member who is unaware of his brothers' true nature. While Iko believes they are a normal, if somewhat unusual, family, his brothers are secretly wizards who possess immortality and live for an almost eternal span. This secret forms the central dynamic of his life, as he is a normal child being raised by extraordinary beings. His motivations are rooted in the simple, everyday joys of a summer vacation with his family, participating in the events of a seaside town without fully understanding the magical world that surrounds him.

The core of Iko's world is his relationship with his four older brothers. Though they have secrets, they shelter, raise, and protect him, and this caring dynamic is central to the family's summer together. The narrative also explores how Iko becomes inadvertently entangled in the whimsical and magical affairs of his brothers. His development throughout the story stems from this juxtaposition, as he is a figure of innocence and normalcy within a family of ancient, magical beings, slowly being drawn into their extraordinary reality.