かくれエッチ

As winter break approaches New Year's, broke college student Sanjou Tomoya hurries home, eager to try out the new porn mag he bought. But the moment he starts getting busy in his room, his stepsister Megumi accidentally walks in. Though she initially freaks out, Megumi — now at that curious age — surprises him by asking to see more. Reluctantly giving in, Tomoya struggles to focus, prompting her to suggest a "show-and-tell" exchange.

The next day, their "momentum" carries them straight into a full-blown affair. Now addicted to the thrill, the siblings seize every chance to hook up while dodging their parents — groping under the kotatsu during family time, ambushing each other in the bathroom, sneaking into baths together, or even fooling around right behind their parents doing dishes while pretending to watch TV.