Saki, my stepsister, loves me with all her heart. She can't bear the thought that I have a girlfriend... But one day, I can't hold back and get caught getting cozy with my girlfriend at home, and Saki sees it... "Fuh~n. Brother has a girlfriend...? Then I guess Saki will steal everything, so much so that you forget about having a girlfriend haha." "Oni-tan, right? Are you a virgin? Wanna practice for your girlfriend?" Pressed by Saki who advances aggressively, my first kiss, fellatio, and even sex happen with her as a stepsister... but this is just practice... it's okay... I thought so... But then, when the drunken girlfriend falls asleep beside me, we have a guilty forbidden sex! "Onii-tan! No! I'm going to come!!" Before I know it, I'm trapped by my little sister... I can never go back to her... "Oni-san, I love you! Let's stay together forever!"