Some TMNT stuff really isn't for little kids.
Chu Hsi was a Chinese-American firefighter who lived in New York's Chinatown district. While trying to save the life of a child he became trapped in a burning building. A mysterious curio shop owner uses an ancient relic to turn Chu into a Dragon so he and the child could escape. He had been empowered by a dragon spirit, which transformed him into the gigantic Warrior Dragon. Now that he was one with the Warrior Dragon spirit, he transformed a second time and assisted the Turtles in battling a giant Foot Soldier, which was impaled on the Statue of Liberty.
Chu Hsi as well as his mentor Fu Sheng were kidnapped by mysterious Ninjas and were taken to Hiroshima in Japan. Their captor Chien Khan sought to bring forth a demon Noi Tai Dar from the underworld. Hoping to channel the energy from a nuclear meltdown he used a spell to brainwash Chu and sent him as the Warrior Dragon to attack the nearby Nuclear power plant. Partly bringing forth the demon he was attacked by it and the spell wore off. Along with the Teenage Mutant Ninja Turtles, April O'Neil and their new ally Ninjara he returned Chien Khan's head quarters and stopped him from making the ritual sacrifice of a girl named Oyuki Mamisha which would fully bring the demon into the world.
As the series progressed, Chu and April O'Neil began dating. Traveling back to New York he helped April defeat Chien Khan a second time. Chu trained with Fu Sheng to try and control his transformations, he began to control his powers better, which included determining the size of his transformation as the situation warranted.