Rintarou Shinjuku embodies Shinjuku Station, designated E27 on the Toei Ōedo Line. His brown hair extends to his neck, complementing distinctive purple eyes and a host-like appearance that mirrors his confident presence. His personality merges narcissism with overt flirtation toward female passengers, though underlying maturity emerges during critical moments. He displays a clear preference for assisting women, initially refusing aid to male passenger Keita Sakuraba due to gender bias in one incident.

Shinjuku has three brothers, though familial specifics remain unexplored. His development unfolds through passenger interactions across episodes. In episode 3, he aids Michi, a young woman pressured into an arranged marriage by her rigid lifestyle and train aversion. Through their encounter, Shinjuku guides her toward spontaneity and railway appreciation, demonstrating his capacity to foster growth despite self-absorption.

A pivotal evolution occurs in episode 9 when Shinjuku overcomes reluctance to assist Keita, an effeminate male passenger struggling with self-acceptance. After initial gender-based refusal, Shinjuku joins collective efforts to support him, contributing to Keita’s realization that authenticity outweighs societal expectations. This marks Shinjuku’s progression toward inclusivity beyond his established preferences.

As Shinjuku Station’s anthropomorphic representation, his character reflects the station’s real-world status as the world’s busiest transit hub, handling millions daily. This connection manifests through his energetic demeanor and alignment with the station’s constant activity and urban vitality.