Man of Many Faces

Man of Many Faces (20面相におねがい!!, Nijū Mensō ni Onegai!!, lit. "20 Faces, Please!!") is a manga by Clamp.

Plot
By day nine-year-old Akira Ijuyin is a normal student at Clamp School, but at night he becomes the mysterious thief 20 Masks. His thefts are usually subject to the whims of his two mothers, which Akira pulls off without any true objections or interactions. One night Akira ducks into the room of five-year-old Utako Ōkawa in an attempt to hide from the police.

Although the pair shares a four-year age difference, they find themselves quickly falling for each other even as Akira finds himself being increasingly more involved with thefts, some of which include Utako's family. This as well as several other obstacles give the young couple's budding relationship a fair amount of difficulty.