Haruma Kawagoe

The main character, a young man who once spoke a prayer to God that his mother would recover after her miscarriage, as well as a wish to Santa that he would "stand in" for her and deliver him a little sister. Years after the wish, it was granted, leaving Haruma with a sudden addition to his household. He apparently cares a great deal for his new sister already and considers her to be extremely cute. (c) Wikipedia