In her ass!

"Cum in my ass John! Do it, fill me with your cum!"

Just then I came, shooting stream after stream of my cum deep into her ass. Her ass sucked out every last drop of cum, and I came for what seemed like forever.

"Oh god... so much cum~"

Power Girl lifted off of my cock, and I could see my cum dripping out of her asshole.

"Phew! That was really something kid! We should do that again sometime. Here, have my number. Call me~"

Then, after we both changed into our respective clothing, we waved goodbye. Power Girl flew off into the sunset, only to be seen several times afterwards because she gave me her number and we are like, totally a thing now.