PGD-847 Tempted by the sister I've always admired who's about to get married... Haruna Yumi

My childhood friend Yui-nee-san, who is about to get married. Her partner is the guy who lives nearby and has been like a real brother to me. They should be a perfect match, but I can't genuinely bless their union... One day, my sister showed me her true face, which she had never shown to anyone before. Her appearance was incredibly lewd compared to her usual pure self... 'I'm marrying that person, but let's have lots of sex?'