Boku ga Tenshi ni Natta Wake
BokuTen: Love Song of the Angels (Trial v2 JPN).
Nestled between the mountains and the ocean somewhere sits the harbor town of Inogo City, a prosperous place with an atmosphere of the exotic. It is this city, watched over by the church at the summit of the highest mountain, where a boy and a girl first meet.
The boy's name is Kirinokojima Tomoe. A lonely young man, who believes neither in love nor in happiness.
The girl's name is Aine. One who sings of love to fill the world with happiness, who was born for that very purpose ... an angel.
Sources:
VNDB.org (read more)
MangaGamer (read more)