The Boy
Name: Shuuichi Minamino
Age: 15-18 (depending on where you are in the series)
Hair: Red
Eyes: Green
Family: His mother (Shiori), stepfather, and step-brother
Personality: Shuuichi is intelligent, soft-spoken, and caring. He's utterly devoted to his mother, even to the point of being willing to give up his life to save hers. He is also very loyal to his friends, and ruthless in battle. He can control plants, like his alter personality, Youko Kurama, although his are not as powerful. And on top of this, he's the top student at his school, Meiou High.
History: After Youko Kurama was gravely injured by a bounty hunter, his soul entered the unborn baby of Shiori Minamino, who named her son Shuuichi. Kurama only planned to stay around for ten years, after which his spirit energy would be recharged and he would be able to return to the makai. However, an event when he was six years old changed all this. While reaching into a high cupboard, Kurama's stool overbalanced, and he fell. Some plates were knocked over and shattered on the floor, and he was heading straight for them as he fell. His mother dived to save him, gashing her own arms in the process. The scars remain to this day. It was then that Kurama started realizing what love really was, and he decided to stay. When his mother became ill, he realized he was "a son who loved his mother," and teamed up with two other demons -- Hiei and Gouki -- to steal the Mirror of Darkness, intending to wish for his mother's health and happiness in return for his own life. Luckily, Yuusuke prevented this by offering some of his own energy as well. After this, Kurama turned himself in, and ended up becoming a teammate of Yuusuke on his Spirit Detective cases.
The Demon
Name: Youko Kurama
Age: 400 (at least)
Hair: Silver-white
Eyes: Gold
Family: None
Personality: Youko Kurama is ruthless, cunning, and merciless. He's downright vicious with his enemies, and seems to enjoy toying with them before he destroys them. He can control all plants, from the simple Rose Whip to the deadly blood-sucking plants that have a taste for demon blood. He also thinks little of abandoning allies if they're in his way or are slowing him down. Perhaps the only person he ever felt any great loyalty for was his partner, a demon named Kuronue.
History: Not much is known about Kurama's early history. He was called the King of Thieves, and one of his favorite pasttimes was cracking magical codes and seals. He lost his best friend Kuronue in a failed heist, when the other demon was caught in a bamboo spike trap and sacrificed his own life in order to save Kurama's. Sometime after this, Kurama himself was grievously injured by a bounty hunter, and forced to assume his soul form and inhabit the body of an unborn baby, thus being reborn as Shuuichi Minamino.