"Daiamondo Heddo" ("Diamond Head") by Misushiro Setona 5 volumes
Nanao is a transfer student in Mehabia Catholic School. There she meets the Judicature Club, a club that conduct hearings and issue verdicts on students' disputes. The story is well written with mystery, comedy, romance and a heartbreaking drama. =( The art seems inconsistent with the characters looking weird at times or maybe that's the point that I missed.