Chai comes from an artificial miniature planet Nobita shaped using the Genesis Diary. He grew up under General Gilmore's oppressive rule; the regime killed his parents when he was very young, leading to his upbringing by an underground rebel faction dedicated to overthrowing Gilmore. Initially marked by crippling fear and hesitation due to his trauma and the rebellion's harsh realities, Chai deeply cares for his comrades and oppressed citizens but struggles with self-doubt about his fighting ability. His life shifts dramatically upon encountering Nobita, Doraemon, and their friends arriving from Earth. Discovering Nobita's Genesis Diary, Chai initially mistakes it for a weapon intended for Gilmore. Learning that Nobita is the creator of their world profoundly impacts him, forcing him to confront his fears and re-evaluate his purpose. The outsiders' determination to help, despite not being inhabitants, inspires him. Throughout the conflict against Gilmore, Chai evolves significantly. He transforms from a hesitant follower into an active, courageous combatant in key battles. His intimate knowledge of the rebellion and terrain proves crucial to Nobita's group. He directly confronts Gilmore, demonstrating newfound resolve and bravery, and actively participates in the final assault on Gilmore's fortress alongside his rebel comrades and the visitors. Following the successful revolution that overthrows Gilmore, Chai embraces responsibilities within the emerging society, actively participating in building a peaceful world free from tyranny. His experiences with Nobita solidify his commitment to protecting his home and its people.