Hakuya Mitsumine

Arriving unexpectedly on Kobeni Yonomori's sixteenth birthday, this mysterious young man enters her life alongside his younger sister, Mashiro. As Kobeni's newly revealed fiancé, he quickly establishes a shared domestic life with the Yonomori siblings. This sudden arrival brings him and Mashiro into the same household as Kobeni and her sister, Benio, fundamentally altering the family dynamic through their unexpected and permanent integration into the home.