Mao Amachi is a six-year-old boy in protagonist Ashibe's elementary school class. His symmetrical black hair forms a distinctive stylized capital M shape across its silhouette and hairline center. He typically wears a light blue T-shirt, dark red shorts, and white socks, with observers noting a visual resemblance to the series' spotted seal pet, Goma-chan.

Mao displays helpfulness by assisting classmate Yuma in forming a peace sign hand gesture to match Ashibe's during an interaction. He regularly joins Ashibe, Yuma, and Goma-chan in group activities and shared adventures.

In Episode 1, Mao facilitates friendship-building between Yuma and new student Ashibe. He walks home alongside Ashibe, Yuma, and Goma-chan, encountering Sakata and Sakata's older brother during the journey, which sparks a confrontation. Mao's involvement occurs within routine school and neighborhood activities.