Occupation: high school student
Birthday: March 3rd
Age: 16-17?
Powers: ability to repel spirits

He's Watanuki's classmate, and some sort of a rival. Those two had never got along, as they have opposite personalities. Doumeki is cool, silent, sarcastic, and he's great at sports, even better than Kimihiro. He also is a part of the archery club at school, and he's quite popular with the ladies. Himawari seems to find him attractive, and of course, that doesn't help Watanuki to like the guy. Let's just say they both annoy themselves mutually, as Doumeki can't stand Kimihiro's loudness and temper.

Shizuka lives in a Shintoist temple. Even if he's almost null to paranormal things, his grandfather (assumable, a priest) could see ghosts and performed exorcisms. He may not be able to see anything weird, but he can certainly repel the strange things our main character is chasen by. And here's the big point: when Kimihiro is near Shizuka, the monsters won't attack him that much, so Yuuko makes them go together to the "missions", which bring some laughters to the reader.

Besides, he has saved Watanuki several times and made important sacrifices for him (and viceversa). With time, their friendship and bond has intertwined deeper, to Watanuki's dismay. I think we could assume Shizuka's feelings for Watanuki should be romantic, as he's usually doing so much for him.