NACR-169 Sneaking into my wife’s sister’s place for sex with internal ejaculation

I’m Yui, a female college student. She went to an amusement park in Tokyo with her boyfriend. I will stay at my sister’s couple’s house at night. My older sister’s husband is in her late 40s, but she’s young and cool, so I’ve admired her for a long time. I’m the exact opposite of him… I envy my sister a little. But she never thought it would happen…