Valentine's Day may be past, but that's not going to stop me from trashing on some poorly conceived harem manga.
PURI PURI, by Chiako Taro. First published in 2005 and first published in North America in 2007.
PLOT:
Shocked by the scandalously sloppy looks and behavior of his students, the principal of the all-girls Saint Sophia's divinity school decides that the best solution is stricter surveillance and to make the school co-ed. That's how Masato Kamioda became the school's first male student, hoping to use this opportunity to study for the priesthood like his foster father. Following in that holy path will be more challenging than Masato anticipated, as when he's not being threatened with expulsion by the student council he's being tempted by the soft, squishy, panty-clad bodies of his fellow students. In particular, the body of sweet, motherly Ayako might be the biggest temptation of them all.