A 25-year-old office lady and her 22-year-old college student brother take part in a game of strip baseball where they compete for prize money. The rules forbid arousal or erection, and failure leads to forbidden punishment games. The sister confidently mocks her younger brother, teasing him into the match despite his nervousness and embarrassment. After repeatedly losing rock-paper-scissors, the sister is stripped down to her underwear, while the brother desperately tries to stay calm. When they use a "help card" forcing them to kiss, the virgin brother sticks his tongue out seriously into his sister's mouth, and upon seeing his semi-erect cock, she snaps, "Why are you hard?!"—half angry, yet slightly pleased. During the brother's turn, he hits his sister with a vibrator, and though she tries to endure it, she moans, "Wait… no, I can't! Stop! Sorry, I can't take it!" as she squirts and orgasms. The sister then proposes a special rule: if she can make her brother's cock go soft, she wins the prize money. "Just don't tell Mom and Dad!" she says, starting to jerk him off. Frustrated by his lack of response, she switches to a blowjob. He cums inside her mouth, but his cock remains fully erect, shocking her. She resumes sucking, but after the second cumshot, his numb cock still won't go down, so she strips completely naked, starts masturbating, and continues jerking him off. Seeing no sign of ejaculation, she leans in with a seductive look and whispers, "What I'm about to do… you'll keep it secret from Mom and Dad? Promise?" She lies back, spreads her legs, and guides his bare cock to her pussy. Losing his virginity, the brother instinctively thrusts like a dog, overwhelmed by the pleasure of her bare pussy. As his sister cums repeatedly, she dares him, "Are you close? Go ahead, cum inside!" and he shoots his load deep into her womb. Even after two creampie loads, his cock stays hard. "Guess I have no choice…" she mutters, mounting him in cowgirl position and riding him hard, grinding her hips wildly. Under the pretense of trying to soften his cock, she indulges her hidden nymphomaniac side, orgasming repeatedly. Pleased with her brother's stamina, she rides him aggressively, pounding herself like a stake, climaxing over and over. "How about from behind this time?" she asks, presenting her ass, and cums intensely as he pounds her from behind, before filling her with another creampie. Still, his cock won't go down. Exasperated, she heads to the shower to cool off, but at her brother's request, gives him one final handjob, making him cum a fourth time. Total: 2 creampie loads, 1 blowjob, 1 handjob—4 orgasms in total!