Tactics is a manga created by Sakura Kinoshita and Kazuko Higashiyama. Taking place in Japan in the 1900's, the show focuses on Kantarou, a young man who can see spirits. Kantarou unseals a powerful spirit and names him Haruka, becoming his master. The two become friends and work together to go after other evil spirits.
As an interesting side-note, the creators of this manga actually made yaoi doujinshi (fan comics) based on their series. This practice isn't uncommon (the creator of Gravitation famously created some very explicit doujinshis based on her work) but it's notable since Tactics isn't considered a BL or yaoi manga.
Both the manga and anime versions of Tactics are available in America. Tokyopop is currently releasing the manga. The anime version, which aired on SciFi's Ani-Monday back in 2008, was released by Manga Entertainment and is currently available on DVD.
