Tsubasa is a young boy from the fictional city of Lost, which vanishes under mysterious conditions. He works as a messenger and courier, leveraging exceptional parkour skills to navigate urban environments during deliveries. His appearance features long black hair tied in a ponytail, typically paired with a violet sweatshirt, white shirt, black pants, and black sneakers designed for movement.

Brave and determined, he frequently assists others despite risks. His loyalty manifests through a protective relationship with Yuki, another key figure impacted by Lost's disappearance. Tsubasa actively supports Yuki’s quest to find her missing father, dedicating significant effort to this goal. After the city vanishes, he establishes the Phantom Thieves, though the group's specific objectives remain undefined.

His background includes being the older brother of Yoshiaki, though circumstances surrounding their separation are unclear. Tsubasa’s combat proficiency complements his parkour abilities, enhancing his effectiveness in confrontations.