Tazuna is a young boy who loves to fix things. But his life takes an unexpected turn when he meets a girl who's lying on a hospital bed in an electronically locked lab. When he takes her hand, he finds out that he can never let go!

Tazuna and his new friend Koyori have a problem: If Tazuna lets go of Koyori's hand, she'll die! Can he take her home with him and explain to his parents why he now has to live with a girl? And how's he going to take a bath with her!?

Tazuna meets Chizuru and Hayate, the pair whose car he fixed on the day he met Koyori. They're workers for a major food corporation in the area, and they offer to treat him and Koyori to dinner as a thank you.

Tazuna and Koyori must come up with a new name for battle while inside the Ziggurat to avoid being found in the real world.

Koyori gets separated from Tazuna, and because she doesn't have a cellphone, she doesn't have a way to get in touch with him. Fortunately, she's found by President Lily and her little brother Masaru, who take her to play a new game.

Lily and Masaru insist on fighting Single Gear, despite Tazuna's fervent protests. The two of them use cards: Lily, her Tarots, and Masaru, his precious memories deck.