Ginrou Kaiki File

This drama makes use of a mixture of high-school detective, a bit of horror and a bit of sci-fi. Kosuke is a young student at a high school who gets involved in an accident with his best friend. Kosuke survives the motorcycle accident yet his friend dies. Waking up reveals though that Kosuke has changed... now one other personality besides Kosuke demands to exist. This other personality seems ready to take over in situations of extreme stress. The sensitive and gentle Kosuke is opposed by his counterpart highly intellectual yet naughty Ginrou. This "transformation" also comes along with an actual change in Kosukes appearance, since Ginrou has curly hair and blue eyes.
(Source: Drama Wiki)