Four suits and a joker

The four-suit structure is the tidiest route architecture in the otome canon: Heart, Spade, Clover, Diamond, with Joker locked behind completion of the first four. Each suit corresponds to a world, not just a boy, and the heroine's amnesia carries different stakes in each — the routes are variations on a theme rather than parallel branches.

The Joker route is where the game shows its hand. Until you unlock it the framework feels schematic; after you play it, the schema turns out to have been load-bearing.