For your mental imagery, my SIL is 30 years old, long blonde hair, 5’5″ 140ish lbs, plump pouty lips, 36DD juicy tits, big round ass and nice plump pussy from what I can tell.
A little backstory before the fantasy. It was the 1st of many occasions I was lucky enough to feel the forbidden fruit of my SIL beautiful booty. She needed some work on her car done and asked for my help. Which I happily obliged. While doing said work I needed her to help with a few things. It was a rainy day and I had her car in my garage. I asked her to work all the lights and she leaned in the door with her ass sticking out at the perfect viewing position for me. So I let her do a bunch of stuff just so I could continue to admire it. Once I didn’t need her help any longer she said “Oh it’s raining hard now!” I got real close to her to look outside and said “Why yes it is.” We stood real close for a few minutes, when I gave her a couple pats on her lovely ass and said ” Hurry or you’ll get soaked!!” After a second she took off running back inside. That’s how that ended… but here’s what my fantasy would look like…