Kaitou Saint Tail is a wonderful manga series from the manga magazine Nakayosi which was made into an anime. The manga has been complied into 7 tankouban, and the anime is 1 season long. If you are a fan of mahou shoujo (magical girl) series, or just a fan of absolute cuteness, you'll love this endearing story.
Fourteen-year-old Haneoka Meimi is a regular schoolgirl attending a Catholic school.... by day. At night she transforms into the magical girl, Kaitou Saint Tail (Mysterious Thief Saint Tail). Her best friend, Seira, a nun-in-training, is the only person who knows Meimi is Saint Tail. People who are sad because something has been stolen from them come to Seira and tell her their problems. Seira relates the story to Meimi, who then steals the item back (hence the name Mysterious Thief).
Asuka Jr. is a classmate of Meimi. A detctive and the son of a policeman, he is intent on catching Saint Tail. He doesn't know, of course, that Meimi is the girl he wants to capture, and she leaves him notes from Saint Tail all the time to let him know where she'll be next. Every night he tries to get her..... but each time he does manage to catch her she gets away or he lets her go. He doesn't realize it, but he really likes Saint Tail, and that is why he wants to catch her, not to turn her in to the police. Meimi has a crush on Asuka Jr. but he is too interested in finding Saint Tail to pay much attention to anyone else. Rina, one of their schoolmates, also has a crush on Asuka Jr. Eventually, she finds out that he really only cares for Saint Tail, and it makes her sad.... and then mad. She decides to catch Saint Tail herself as revenge. Meanwhile, Sawatari Manato, a tan-haired boy who takes pictures all the time, has a crush on Meimi. He tells her funny things like saying she is the princess of legend and stuff.
Saint Tail has a friend that often accompanies her on her stealing trips - Ruby, a cute hedgehog.