Ryuunosuke Fujita wants nothing more than a fun and carefree life with his friends. But life doesn’t always turn out the way you want it to. When the third-grader comes home one day, his father introduces him to Koharu Mori, a young girl in a wheelchair with prosthetic limbs who will be Ryuunosuke’s younger sister from now on.
For Ryuunosuke, this means that he must constantly take care of her and has no time for himself. Although he understands Koharu’s situation, Ryuunosuke begins to loathe her and the responsibility that threatens to rob him of his youth.
However, Ryuunosuke soon finds that his everyday reality is being replaced by fantasy. When he finds Koharu floating in the air one night, they are suddenly attacked by a nightmarish creature from his imagination. After his father eliminates the monster, he reveals that Koharu is actually a divine being.