Hajime Yasaka, a 13-year-old boy spending summer at his grandfather's small town home, encounters Sayoko Arashiyama (Arashi) working at the local café, Ark. Touching her hand forges a "connection" enabling mutual time travel, vital for Arashi, a WWII ghost, to rescue people from wartime air raids.

Energetic and brash, Hajime champions traditional masculinity and chivalry. He develops an instant infatuation with Arashi, captivated by her beauty and kindness, yet struggles to voice his feelings. Initially skeptical of the supernatural, witnessing Arashi's powers swiftly convinces him. His experiences foster maturity, including confronting jealousy towards Takeshi Yamashiro, a man Arashi saved in childhood who embodies an idealized "perfect man" through wealth and demeanor.

Time-traveling with Arashi reveals intricate temporal bonds. During a 1945 trip, Hajime shelters a child in an air raid, urging him to become a hero; this child grows into Murata Hideo, a present-day private investigator. Hajime also learns he himself, as a time-tripper, was Arashi's first love. His actions inadvertently create paradoxes, like causing object disappearances by interacting with his past self.

Beyond Arashi, Hajime forms key bonds. He befriends Jun Kamigamo, who cross-dresses as a boy; Hajime remains oblivious to her true gender despite incidents like body-swapping and seeing her undressed. Later, Jun develops romantic feelings for him. He also connects with Yayoi Fushimi, another ghost; their link stabilizes her weakening ethereal form, enabling joint time travel.

Hajime supports other arcs, working at the café alongside Arashi, Jun, and the con artist owner, Sayaka. His presence aids conflict resolution, such as helping restore energy to the ghosts Yayoi and Kanako Yamazaki, who initially drain Arashi's vitality to sustain themselves.