Daichi Arai is one of the two protagonists in the anime short film Bâan -The Boundary of Adulthood-. He is a 21-year-old Japanese man who finds himself at a significant crossroads in his life immediately following his graduation. The central conflict driving his actions is a deep-seated restlessness and a desire to break free from the expectations placed upon him by his family. Specifically, Daichi experiences conflicts with his family and chafes against what is described as their overprotectiveness. This pressure is further intensified by the expectation that he will enter the family business, a path he feels compelled to reject.

Driven by a powerful motivation to forge his own identity and find a place where he truly belongs, Daichi makes a radical decision. He chooses to leave Japan behind and travel through a mysterious warp gate to the fictional world of Euthania, a fantastical realm rich in nature and inhabited by various magical races. His journey is not one of a powerful hero but rather a personal quest for a freer and more independent life, representing a physical escape from the societal and familial pressures he feels at home.

In the story, Daichi’s role is to represent one half of a thematic parallel, as his journey to Euthania is mirrored by the other protagonist, Rinrada Ratchamanee, who travels from Euthania to Japan. His narrative arc focuses on the expatriate experience and the process of building a new life in an unfamiliar culture. Initially, Daichi is portrayed as a self-sufficient loner; he starts his new life by camping alone in the wilderness outside a village. His personality is marked by a determination to be independent, but his development throughout the story shows a gradual shift. Over time, the hermit-like Daichi begins to integrate with the local community of Euthania, finding a sense of connection and belonging he was missing in his own world. This evolution illustrates the film's central theme that the search for a home is a personal journey, and that finding a new community is a vital part of adulthood.

Regarding his key relationships, the most defining is the strained dynamic with his overprotective parents, which serves as the primary catalyst for his departure from Japan. In Euthania, his relationships start from a point of isolation but evolve as he forms connections with the villagers, moving from an outsider to a member of the community. There is no information available about notable or unique abilities possessed by Daichi; his character is not defined by supernatural powers or combat skills, but rather by his relatable, grounded struggle for autonomy and self-definition.