Mawang IlgiDemon Diary - Lee, Yun-hee

Gods and demons wage a neverending battle with the mortal realm as their battlefield. As with most longstanding feuds, the reasons are no longer important--hatred is a way of life. But it is foretold that one would arise who could restore harmony between gods and demons. Enter Raenef...heir to a set of demon royalty, he is hardly courtly material. The demon king assigns Eclipse to be his tutor, to mold Raenef into proper demonic shape. The two begin a journey of discovery and are soon joined by a human knight and a god-blessed priest.

(Source: Tokyopop)
Included one-shots:
Volume 1: Crystal Heart, Tera

Mawang Ilgi was published in English as Demon Diary by Tokyopop from May 6, 2003 to May 11, 2004.