NSFW// KAJFJFK YES-
Theres two options for this one cuz my brain enjoys both equally
1. Unit swap au (Saki, Tsukasa, Toya, Honami)
After they finish practice, honami decides to take everyone stargazing on the roof. Saki keeps tsukasa behind, pretending that she got an urgent text from their parents so nobody would suspect them. Locking the doors, she pulls a desk out and sits on it, legs spread wide as she beckons her brother over. Unable to resist her, Tsukasa pulls her in and kisses her with a burning passion, their tongues mixing as they share spit. One thing leads to another and Tsukasa finds himself inside his sister, still connected at the lips, desperately devouring her. As Tsukasa pumps into her, making her whine and cum like a whore, Toya looks into the window of the classroom on his way to collect his things so that he can go home, and ends up traumatised, yet unable to look away, as he watches his chosen siblings fuck.
2. No au but canon divergent
Saki wakes up feeling needy, a heat in her body pooled between her soaked legs. This is the first time shes truly felt like this. Before she had only ever accidentally happened to see her brother in the shower or felt embarrassed yet tingly in the girls changing rooms, not realising she was staring at Honami’s boobs. No, this was different. Her panties had soaked through to her pyjama pants, and her whole body felt like pure electricity. Trying to touch the source of her… problem only made things worse. Waking from a dream where her brother bent her over the kitchen counter, touched her girly parts in the shower and rakes her insides, sucked on her breasts backstage after a show and licked her kitty until she writhed and screamed was FAR different than having a sexuality crisis over your best friend or walking in on family showering. She needed to sort this. After changing into something else and putting those pyjamas into the wash, she went upstairs and hammered on Tsukasas bedroom door. Without waiting for an answer, she barged in on her brother rehearsing and pressed play for NeedLe, the blinding light dragging her and her brother into the school sekai. Before he even had the chance to ask where he was, or what she was doing, Saki kissed her brother. Desperately. This was different to the kisses they shared when they were younger. Those were innocent, sweet and gentle. This was violent, crazed, and craved satiety. Tsukasa, now with a tent pitched in his pants, kissed back, his tongue dragging along the roof of her mouth, biting her bottom lip with a gentle suckle, and dragging her tongue into his mouth for the occasional suck. This was it. This is what Saku’s body craved as her weakened knees caused her to lose her balance, toppling them over and causing Tsukasas painfully hard cock to rub against Sakis dripping wet pussy. Both found a surprisingly fast release as Saki ground down, still linked as lovers are - by the lips.