Yuya Kitaoka (Ryuki Takahashi) is a high school student. One day, his mother suddenly introduces his younger sister to him. Her name is Mirai (Risa Taniuchi). She possessed magic powers at one time, but does not anymore. Mirai is a lonely girl. Yuya is confused by the situation, but they live together as brother and sister. Mirai gets used to her new life, but ..

悠也（高橋龍輝）は元魔法少女のみらい（谷内里早）を、妹だと紹介されて一緒に過ごすようになってから半年が過ぎようとしていた。シングルマザーの母は仕事で留守がちなため、高校生の悠也が妹の面倒を見ていた。彼は奇妙な共同生活に違和感を覚えながらも、幼なじみの千花（森田涼花）らと相変わらずの日々を送っていたが……。