The protagonist lives with his sister Kaede due to their parents convenience, at school he is an honor student with excellent grades. On the other hand, he is a serious siscon and loves Kaede from the bottom of his heart. Although he realize that this is an unfulfilled wish, he wants to make Kaede his own someday and love all of Kaede.

One day, when he tried to pick up the smartphone he dropped in the plant while he was at school, he was injured by a bug and got a small wound, but the wound disappeared as if nothing had happened immediately. After that, something strange happened to the heros body...