My Sister is My Girlfriend!? Sexual Relationship for Two Nights and Three Days

I'm going on a trip with my sister for two nights and three days and having sex with her!? At the order of my sister, Nonoka, I ended up traveling in a group while pretending to be her boyfriend. We were trying to act like a couple and flirt, but when my sister's boobs and butt touched me, I was turned on immediately! We slept in one bed like a couple would, and I was losing my reasoning! "We're just acting! We can't do this! Stop teasing me with your fingers while licking my boobs! I'm gonna cum!" Nonoka was always strong, but was I going to lose to her foolishness and have sex with her for the first time!?