D.O.B: 27th December
Blood-Type: O
Height: 180cm
Weight: 70kg

Plot:
Yukio is Rin's younger twin brother.
When it was discovered that the woman impregnated by Satan was going to have twins, it was believed that Satan's powers would be split between them. Due to the weakness of Yukio's body, however, he did not inherit any of Satan's powers, thus being born fully human with the full extent of Satan's powers going to Rin.
Yukio did, however, receive a spirit wound at birth from his brother, which allowed him to be aware of demons for as long as he can remember. Yukio secretly trained to become an Exorcist from the age of seven in order to protect Rin through the help of Fujimoto. Even though he and Rin argue a lot, Yukio truly cares about his brother. Fearing Rin will be consumed by his demonic nature, Yukio often berates him for his impulsive actions and reckless attitude.

Abilities:
It is often stated that Yukio is considered a prodigy, having already acquired the title of "Meister" in both the Dragoon and Doctor class, while ordinarily most people would aim for Meister in only one class (both are still fully qualified exorcists). He is currently ranked a Middle First class exorcist.
In combat, he dual wields pistols.

Source:Wikipedia