With Japan in the midst of a bloody revolution, an elite cadre of samurai swordsmen known as the Shinsengumi must protect the embattled city of Kyoto. Tetsunosuke Ichimura has spent his life dreaming of working at the Shinsengumi, and his wish has recently been fulfilled. As a page for Vice-Commander Hijikata Toshizo, he is privy to a wealth of secrets and is among Japan's highest ranking officials, some of whom are actual historical figures. When a strange gun-toting swordsman, Ryoma Sakamoto, recognizes Tetsunosuke and his brother as the sons of someone he calls the "Peacemaker," trouble brews and the other Shinsengumi run the outsider out of town. Full of action, this sword-fighting and gun-toting story is centered on the bakumatsu, a chaotic and bloody time of revolution that would ultimately result in the disbanding of the samurai and the opening up and Westernization of Japan. Fifteen-year-old Tetsu must witness the war around him, and perhaps gain some amount of wisdom about the samurai.

When childhood innocence gives way to a blinding thirst for revenge, is it worth the price of one's humanity? Tetsunosuke and Tatsunosuke are the sons of a diplomat who sought to bring peace and prosperity to Japan during the early Meiji Restoration. But when their parents are murdered before their very eyes, Tetsu seeks to join the Shinsengumi, the unofficial police who are capable of the same brutality as his parents' murderers. Wading through a sea of espionage, deception and bloodshed, the young boy must choose: should he take a step on the path to becoming a demon...or give up his rage and transform into the ultimate Peacemaker?
(Source: Tokyopop)

Kokonose is an elementary school exorcist, and he's evil to the core. Stranded on a remote island, he ends up going to an elite school for demon hunters. (Source: Hana-mi)

Charley is a cyborg vampire Jesus freak who does the Vatican's dirty work. Johnny is a vampiric hedonist who loves irritating his more-or-less unwilling partner. Technically not yaoi, but almost.
From
-------Hanami

* The second volume of Vassalord contains a bonus one-shot story in the back called "Zoul Harf" or "Zoul Half". This special one-shot was first published in the Comic Blade Masamune summer issue in 2003*