Mangaupdates:
Teacher Hisoka wakes up to find that he has died and is now inhabiting the body of the student he tried to save. This is due to the interference of a monk, who informs him that he cannot tell anyone who he really is or the bond between him and his "new" body will break and he will die for real. Hisoka chooses to retain his memories despite the monk's warning that it will cause trouble....No doubt it will, since Hisoka is the type who cannot pass someone in trouble without trying to help!

EDIT 12/18/2014: There's an complete, official and free web scanlation of this manga that can be found here: http://en.mangareborn.jp/creation_series/978