Seto no Hanayome OVA

Synopsis

new semester begins where Nagasumi, San, and the others are third-grader seniors. Everyone got into the same class except Nagasumi got sent to the eighth middle school, class zero where in a classroom full of delinquents. Unable to cooperate with his new class, their homeroom teacher Shark Fujishiro plans to make a killing spree session on his first day of homeroom. Meanwhile, a new student has come to Sun and Lunar's class who turns out to be Lunar's Papa who is dressed in a female middle school attire along with an apron. This disgusts Lunar and makes a whole ruckus in the class. When Seto Gozaburo asks them to quiet down, Lunar's father tells him to not interfere and the two start a fight. Lunar and Sun leave to find Nagasumi and get him back to his seat to clear their situation.

(Source: My Bride is a Mermaid Wiki)