Luna Lunatic Mangaルナ・ルナティック, , 校園之吻
16 year-old Luna is a first-year student at Angelica High School, run by Catholic nuns. Luna's a cute girl, but she gets in trouble a lot for her behavior. For example, during church services, she hid in the back asleep and drooling instead of paying attention.
After one such bout of bad behavior, Luna is punished by having to clean the church. As she does, she pauses to examine a beautiful piece of art on one of the walls. It's like a stone carving where a man's body is coming halfway out...
Click to read more here