Manga with a boy saving a girl from monster attacks by playing music, is accompanied by a fairy

All I know about it is this:

• A young girl was roller skating and attacked by a monster.
• She was held captive then saved by a boy who helped by playing music who transformed and managed to defeat the monster.
• A couple of pages later it happened again this time at an ice rink and once again she got caught and saved by the same boy who played music on a piano and he’s accompanied by a fairy I believe.
• I don’t know exactly what happened next but all I know was at the end the girl, the boy, and the fairy saw a entity and the fairy said "that’s a demigod" or something.