Leyu Yoshida and her brother Shiro were born to a woman who suffered radiation poisoning due to exposure to the atomic bombing of Hiroshima. As a direct result, they were born mutated, possessing identical powers. Shiro went on to become the famous X-Man, Sunfire.
When Magneto was bent on starting World War III with his mutant army from Genosha, Leyu appeared and joined the X-Men. Jean Grey had summoned Sunfire, but instead Sunpyre appeared, as Shiro was at the time unavailable. Sunpyre impressively battled Magneto, but almost was defeated when he created a metallic cocoon around her. Later, Sunpyre chose to return home instead of remain in the United States with the arrogant X-Men.
Banshee later invited her to join his X-Corps. She spent most of her time in the laboratory studying the mutant, Abyss. However, Mystique had infiltrated the group and began her plan for taking over the X-Corps. Mystique stabbed Sunpyre to death, and also stabbed Banshee.
Later, a Sunpyre from an alternate reality was pulled out of Honey Lemon's Power Purse to fill Sunfire's spot on the Big Hero 6 team. In response, Sunpyre worshipped Honey Lemon like a goddess.