College student moves in with sister-in-law, sparks fly, secret affair ensues

After his brother accepted a long-distance transfer, college student Tsutomu moved in with his sister-in-law, Mai, to help out with the flower shop. But he has a secret... he's always been in love with her! Late one night, Tsutomu kisses Mai and they end up in bed together. Even though Mai says it can only happen once, she can't help calling out his name the next night as she fucks herself with a vibrator loud enough for him to overhear! Until her husband comes home, they'll sneak in all the kinky activities they can at the flower shop... but pretty part-timer Kozue is quick to notice something's changed...