From Tokyopop:
An introspective, character-driven series, Tokyo Babylon reads like a manga version of The X-Files. Its story -- a modern-day fantasy -- follows a young onmyouji (spiritual medium) on his quest to protect Tokyo from evil spirits.
Teenaged Subaru Sumeragi is the 13th head of the Sumeragi clan. Together with his twin sister Hokuto and the mysterious veterinarian Seishirou, Subaru travels around Tokyo, calming the ghosts that threaten the city.