Yuuko is a mysterious girl who Hiro first meets in a church during the Christmas night. She always appears generally out of no where. And she disappears just as quickly in various places throughout the story. Yuuko always talks to Hiro or to other characters to give them advice. It it also shown that Miyako already knows Yuuko.
Yuuko is a main character for ef: Tales of Melodies, and is focused around her connection to Himura, when they were young. She is a kind hearted person who hates being alone and puts on a brave face, even when upset or hurt.