Immortal Rain

Immortal Rain (メテオ・メトセラ, Meteor Methuselah) is a shōjo manga created by Kaori Ozaki. It was first published in the Japanese monthly anthology Wings as Meteor Methuselah. As of September 2007, the current eight volumes have been published in English by Tokyopop, with the rest of the series when published in Japan, expected to follow. The 10th volume has recently been released in Japan. It's published in French by Doki-Doki.

Plot
Rain Jewlitt, known as the Methuselah, is a spaced-out, immortal, 624-year-old man dressed in priest's clothes. He's got eternal youth and a large price on his head ... put there by those questing after the secret of his immortality.

Machika Balfaltin is a tomboyish, energetic 14-year-old girl who, upon the death of her grandfather, sets out to kill Methuselah, the one bounty her assassin grandfather, Zol the Grim Reaper, couldn't kill. Instead, however, Machika ends up being saved by Rain again and again from other aspiring bounty hunters attacking them both.

Other Sources

 * Immortal Rain
 * Immortal Rain Manga on AnimeNewsNetwork