Nanji, Chikai no Kuchizuke wo...

No one knows that 1st year Rena (16) and upperclassman Kyouta (18) are in fact married. This manga follows them in their lives to discover more about each other and keep the fact they are married a secret from everyone at school. They'll be tested in Jealousy, love confessions, exams, love, mother in laws, embarrassing situations, noisy neighbors and teachers.
(Source: Onigiri-Gakuen)