The main male protagonist, a first-year high school student. Troubled by an accident involving his younger sister and rejection by his anguished mother, he currently lives at his grandmother’s house. Due to that accident he possesses a gloomy attitude. One day in mid-winter he becomes involved in the struggle to protect the world, together with Lisa. Source: Japanese Wikipedia
Later on in the story it was revealed that he once met Lisa when he was still a child, and had a much more cheerful personality back then. It was because of this encounter which changed Lisa to what she is now.