First time I think Maruyama has a legit grievance. The missing slipper was pushing it a little too far.
Also further establishes his bro status seeing how distressed he was when he couldn't find Mamoru.
Maruyama is made up of 50% loyalty to his friends and 50% sexual perversion. When he sees the incredible woman next to him, his perversion will be diluted. The new composition will be 40% loyalty to friends, 10% sexual perversity and 50% love.
Not cool. At least in México doing that to family or friends has send people to the hospital for the stress or a heart attack. The reasons to be worried are plenty.