Hakase Mizuki manga
From Tokyopop: A lonely yet caring 15-year-old Chiaki, the half-angel daughter of the Archangel Michael and a human woman, welcomes into her home a dejected devil Ororon who pledges to stay at her side forever. Both of them have been ostracized from their respective celestial realms--Chiaki because her origins are impure and Ororon because he is the youngest son of the Lord Devil and therefore a threat to his older brothers for leadership of the underworld. As various agents of heaven come by to destroy the angel Chiaki, she learns that having the incredibly powerful Ororon by her side is useful. And as assassin after assassin comes to eliminate Ororon, he learns that Chiaki can teach him a valuable lesson about the sanctity of life.
From Tokyopop: Long ago, when Japanese gods descended upon humans, their mixed offspring inherited supernatural powers...and the name "Kuruizaki no Hana." Now, those of the Demon world are rising up to wipe out these offspring - led by the cool and confident assasin, Ushitora. He's worshipped as a deadly professional, but when he falls in love with one such gifted boy, Masato, everything changes. Ushitora betrays his people, instead sacrificing himself to a life on the run, in order to care for Masato and a spirited orphaned girl named Nao.
From Tokyopop: In this collection of paranormal short stories, Takeshi Uesugi finds out that he is the reincarnation of the "Baku," a spirit that devours people's nightmares, while Mephist 'helps' ghosts, demons, and other supernatural spirits. Everyone has a past or memory they can't forget in these terrifying tales of the supernatural!