We never learn 4.

Ms. Kirisu may not approve of Yuiga tutoring Rizu and Fumino, but that doesn’t matter to him! He’s dedicating to helping not just them, but Ms. Kirisu as well! When he discovers that her apartment is a wreck, he becomes determined to clean it up. Add being trapped in a store mascot costume, cockroaches, impromptu dates and a trip to a maid café and Yuiga is in for a raucous time!