After working late and missing the last train, the older sister is invited into her younger brother's apartment. This situation has happened several times before, and as usual, he offers her the living room to rest. The sister says she still has work to do, turns on her laptop, and begins working. When the brother heads to the bathroom, he notices his sister has fallen asleep—she must have dozed off while typing. The kind brother decides to cover her with a futon, but can't help noticing her thighs. Being a man, he can't resist the temptation and starts touching his cock through his pants. He begins masturbating while gently stroking her thighs. As he rubs his cock against her thigh, the sister wakes up. In that moment, he presses against her more boldly. "Hey, what are you doing?" she asks in shock, naturally getting angry. The brother panics and tries to make an excuse. But seeing his expression, the sister suddenly smiles softly and says, "Oh, right—you still don't have a girlfriend. Can't blame you, you're a guy after all. Big sister will help you out." She begins by jerking him off, then moves on to a blowjob. When he still can't cum, she says, "We're siblings, so I can't let you inside, but I can let you rub against me. Just come like that." She starts grinding against him through their underwear. Even through the fabric, the sensation gets to her—she admits, "Big sister's getting wet... My panties will get dirty, so I'll take them off." She removes her panties and then her skirt, straddling her brother's hips. As she gets more turned on, she opens her blouse and lets him grope her breasts. Continuing the grinding with saliva smeared between them, their passion builds. Accidentally, she ends up taking his cock inside, and though she notices, she lets it happen. She clings to him tightly, grinding her hips wildly as pleasure surges. Finally, they end up in missionary position, and the brother accidentally cums inside her. "Sorry, sis..."