Yamada-san is good at cuckolding

Morisaki Shirou loves his cheerful gal girlfriend Rikka enough to push her into sleeping with other men, and that's the whole engine of this one. He gets off on the jealousy as much as the guilt, and so does the story.

The plot sticks close to that arrangement. Rikka gives in to the men Morisaki arranges for her, he stews in envy and arousal in equal measure, and the two of them keep circling back to each other at night to prove the relationship still means something. It's a school-set romance that treats infidelity as the whole point rather than an obstacle to fix.

There's no real gameplay layer beyond reading the fallout of that arrangement and choosing how far it goes; the multiple endings hinge on whether you can stomach the ending you're steering toward. Combat and puzzles are not on the menu, and nobody pretends otherwise.