Tsukasa's a detective. He's a pretty friendly person, but always acts serious at work. Lately, his team has been working on trying to catch a sneaky thief: Rui Kamishiro. That crook always escapes right from between their fingers. And what's most strange, he always sends letters to Tsukasa after every stealing he does. But these aren't threats or mocks, they're love letters. The detective tries to ignore them, yet they sometimes have light hints on his next robbery, but they're hard to decipher.