Ginjirō Sannomiya is an eleven-year-old fifth-grade student and a supporting character in the anime First Love Monster. He is one of the friends of the main character Kanade, belonging to a small group of classmates who are all notable for looking significantly older than their actual age.

In terms of physical appearance, Ginjirō is tall for his age, standing at 178 centimeters or about five feet and ten inches, with a slender build. He has navy blue gradient hair that reaches his neck and teal eyes, which are typically hidden behind a pair of dark-framed glasses. His outfit often consists of a white t-shirt with a red bow tie, a light blue sleeveless sweater with red stripes, matching dark blue shorts and socks, and brown shoes.

Ginjirō has a calm and generally quiet demeanor, which makes him come across as considerate to those who know him. However, he has a well-defined eccentric side. He is an outspoken individual when it comes to immature or perverted topics, frequently discussing such matters with a completely straight face. This behavior leads many of the girls in his class to label him as creepy. Among his immediate friends who all look like older teenagers, he is noted as the one most in touch with his burgeoning sexuality. Beyond this, his personal interests lean heavily toward science, specifically the fictional aspects such as aliens, robots, and the occult.

No reliable information is available in the search results regarding his specific motivations, individual role in driving the story forward, character development over the course of the series, or any notable abilities. Similarly, details about his key relationships outside of his friendship with Kanade and his other classmates Tomu and Kazuo are not present in the verified data.