Seishirou Sumeragi is a fictional character from the manga and anime series X/1999, created by CLAMP. He is a powerful onmyouji, a practitioner of traditional Japanese esoteric cosmology, and serves as a key figure in the story's conflict between the Dragons of Heaven and the Dragons of Earth. Seishirou is known for his calm demeanor and exceptional skills in manipulating spiritual energy. He has a complex relationship with Sakura Kinomoto, a central character in the series, and his actions significantly impact the narrative's progression and themes of fate and sacrifice.