Junichirou Uchida, Sara Uchida's younger brother, shares a strong family resemblance with her and their mother. He possesses a hot-blooded, impulsive nature that frequently plunges him into dangerous situations, resulting in physical harm like beatings by thugs.

Allied with the Yakuza's Aoba group alongside Takao "Taka" Itou and Saburou – an association not entirely voluntary – Junichirou views Taka as a mentor and older brother figure. He refers to Taka as "Aniki" and places deep trust in him, solidifying Taka's role as a Big Brother Mentor.

Junichirou's impulsiveness manifests when he attempts to rescue Sara and Akiko Hashou from attackers but is overpowered, requiring Taka's intervention. This pattern repeats later, leaving Junichirou with a broken hand. While Taka transports him to the hospital for treatment, the Great Kanto Earthquake of 1923 strikes, intensifying their peril.

Following the earthquake, Junichirou flees Tokyo with Taka to escape pursuing Yakuza. This necessitates abandoning Sara, contributing to the narrative's bittersweet resolution. Their departure occurs after a decisive conversation with Kiyokuni Saionji, with Junichirou and Taka leaving by boat.