Frustrated by the stalled progress of her own divorce, Rika has begun to play strange pranks on Mahiro when Natsuko is not around, as a way to relieve stress.
Mahiro is confused when Rika calls him a pervert or treats him like a pervert just for touching him lightly or seeing him changing his jacket.
What's more, Rika uses this as an excuse to order Mahiro to do shopping or run personal errands for him, using him as a convenience, behind Natsuko's back.
Since it's not violent or insidious harassment, he can't bring himself to tell Natsuko, and instead, fearing that she will tell him off, he runs away from Rika, who finds it amusing and sets one naughty trap after another.
But Mahiro comes up with a plan to get revenge on his daily grudge.

[From Dlsite]