Isao Shimoji is a first-year high school student and a classmate of the main protagonist, Teruaki Nakamura, as well as Hina Kyan. He is a native of Okinawa, which is reflected in his speech, as he frequently uses the general Okinawan dialect. His proficiency in the Uchinaaguchi language is considered to be at a level two out of five.

In terms of appearance, Isao is tall and has a somewhat intimidating look, characterized by spiked reddish-brown hair and a visible scar located under his left eye. However, his personality stands in stark contrast to his tough exterior. He is known within his class as a cheerful and energetic mood-maker who helps to create a lively and friendly atmosphere.

Isao is an active participant in local cultural traditions. He is a dedicated member of a youth group that performs the traditional Okinawan Eisa dance, where he takes on the role of a taiko drummer and serves as a central, leading figure in the group. His connection to regional customs is further demonstrated by his surname, Shimoji, which is known to be the most common surname on Miyako Island, suggesting he has roots there. This connection is highlighted during a summer test of courage event, where Isao participates by dressing in an elaborate costume as Paantu. Paantu is a traditional and fearsome-looking visiting deity from Miyako Island believed to ward off evil spirits. Isao takes on the important role of this guardian spirit to chase away malicious forces as the grand finale of the event. His performance is so convincing and frightening that he ends up genuinely startling Teruaki Nakamura, who is not familiar with Okinawan culture, far more than intended. Through his actions and personality, Isao serves as a bridge to the unique cultural traditions of Okinawa within the story.