[Singleton (Azuma Yuki)] Yousei no Tawamure [WhiteKnight]

Identical twin schoolgirls Michiki and Miyuki decide to put their sole male classmate through a very particular "special training" after he mistakes one for the other, teasing that it's a teacher's responsibility to recognize his students — even if they change their hairstyle. They strip off their uniforms, keeping only their thigh-high stockings, and the real lesson begins: a blindfolded comparison of every soft, trembling curve, with one twin cooing "Touch it more, remember this is Miyuki" while the other presses forward, slick and eager to be tasted. "Sensei, you can find it immediately even without looking," she whispers, guiding him between their legs until the only thing left to do is tell them apart by sensation alone. What follows is a breathless, dripping contest of pleasure — thighs clamping around his head, breathy moans of "Ah-AHHH" and "Hiy-Aaah," and twin bodies arching in perfect, mirrored sync as they make him prove which one he's learning and which one he's already memorized.