Junna Toono is the main protagonist of the story, a student at Sakurahama Private High School. He leads what appears to be a peaceful and pleasant life living together with his twin sister, Senna, following the tragic death of their parents in a traffic accident. The same accident also robbed him of his memories of the past, leaving him to build his present life from a fragile foundation. Despite this severe past, Junna is described as a very popular boy among his classmates, admired by both female students and some of his male peers.

Junna's personality is defined by his caring relationship with his sister. He is dedicated to Senna, and the two support and rely on each other, with Senna being very fond of her Onii-chan. Their daily life together is so pleasant that it allows Junna to temporarily forget the difficulties he has endured. However, a sense of inner conflict begins to surface as the story progresses. He starts to recall the memories he lost in the accident, and this process throws his emotions into turmoil as he is tossed between his past, his present, and his uncertain future. He faces a difficult internal struggle, realizing that uncovering the truth might threaten the happy days he currently enjoys with his sister.

As Junna's memories resurface, his role in the story expands beyond that of an ordinary student. He discovers that the reality he lives in may be the result of a wish granted by a mysterious dial, a relic that his father found at an excavation site. This revelation forces him into a central and difficult decision. The truth is that in the original world, his twin sister Senna died before she could be born. To be with her, a younger Junna made a wish for her to exist, which created the world he now inhabits but came at the cost of his parents' lives and altered the reality of a girl named Haruhi, who is destined to be closely intertwined with his fate. Junna learns that the current world, where he and Senna are together, is unstable because two realities cannot coexist. He is given a painful choice: remain in the world with Senna or return to the original world where his parents are alive and Haruhi is his sister, but Senna would cease to exist.

Key relationships define Junna's journey. His bond with his twin sister Senna is the most central, built on mutual support and protection. This relationship is tested when he learns the supernatural truth of her existence. Junna also has a deep connection with Haruhi Inohara, who transfers to his school and claims to be his childhood friend. It is eventually revealed that Haruhi is actually his younger sister from the original world, making all three of them siblings in a complex, reality-bending sense. Another important figure is Tomo Kishida, a calm and reserved girl who is later revealed to be the Keeper of Time. She guides Junna, explains the nature of the distorted worlds, and presents him with the critical choice he must make.

Throughout the narrative, Junna experiences significant development. He begins as a content amnesiac, content in his present life, but is gradually forced to confront the hidden truth of his wish and its consequences. He struggles with guilt and anger, particularly when he lashes out at the pain his wish has caused, but ultimately he seeks a solution that avoids complete loss. He does not possess supernatural combat abilities or physical prowess. Instead, his notable ability is his connection to the wish-granting dial. Having used it once as a child, he is ultimately able to understand how it works and use it to form a new, final wish that seeks to resolve the conflict without destroying any of the people he loves. His power lies in his resolve to face the consequences of his past desires and to make a selfless choice for the future.