Kazuki Himura has recently returned to his homeland, Kimikage Island, and transferred to Himeyuri Academy. He comes from a family that has some connection to ancient clans of the island. But the young boy is more interested in the female population of the Academy, especially after he is invited to a female-exclusive club, all five members of which are pretty young schoolmates. Further course of action is clear: seduce all the five girls, to have some really good memories from the school years in the future!
SchoolMate is similar gameplay-wise to other recent Illusion games (such as Oppai Slider 2), having interactive sex scenes and not including any other kind of gameplay. The story of the game is told in text and 3D images of characters and backgrounds; the player has no control over it. At certain points, you'll be able to choose a girl to seduce. You needn't accomplish anything in the game in order to reach the sex scenes, they appear as part of the story.
The sex scenes, like in many other Illusion games, allow the player to physically interact with the girl. Choosing menu commands (combination of actions and body parts), you click and drag one (or both) of the mouse buttons to perform the desired action. Direction and speed of the action is reflected in the real time 3D animation on screen.
SchoolMate uses cel-shaded graphics, and the girls look more similar to classic animé art than to realistic models, as seen in Illusion's other games.