Tatsuki’s imouto Kotoko is striken with an incurable disease and spends every day in her room reading books. He told himself not to enter her room to avoid giving her any stress. One night, he saw lots of shooting stars in the sky and wanted to let her know since she loved seeing pictures of stars and space. When Tatsuki opened her door, he found Kotoko without any vital signs. He blamed himself for causing her death. On another day much later when the night sky was full of shooting stars just like that fateful day, he visited her room just like before. To his surprise, Kotoko was there. The next morning, his parents thought that Kotoko had never died, and for some reason, his pet cat turned into a catgirl.