Power Girl is your Sexual Conquest!

"...you won me," Power Girl says.
"Oh...I see. So if I'd lost..."
"Then you'd be my Sex **** for a Week, yes. Now I'm your's...dammit."
"Don't worry. I'll make sure that you enjoy it."

As you and the Heroines all start to get dressed, Wonder Woman explains the rules of this...

Like normal Bondage ****-Owner Rules, you use safe words and submission. You can't harm her (not that you would) and you shouldn't interfere with League business for this.

In other words, if Braniac conquers the Earth because you were busy fucking Power Girl while she was trapped in Inerton Stocks, it would be bad for *many* reasons.

Power Girl seems nervous, but a little excited too.

The next day, you start to plan what you are going to do with a busty Superheroine Sex ****.

Got it.

Since she was busy anyways (Solomon Grundy is back, so it must be Monday), you arrange a visit to the DEO (with Supergirl's assistance). You invite Power Girl, explaining that your week as her Master begins on the first day of service.

The next day, a well-rested Power Girl meets you at the DEO with Supergirl. She escorts you to their Training Room, which you know is set up for what you want.

You bring a bag of gear, which you explain as sparring equipment. Supergirl vouches for you and guarantees your privacy.

Both of you enter the room and it is locked from the outside by Supergirl. Only she is watching the Monitors.

"Why did you bring me here," Power Girl asks, "Why not my Apartment? Or yours?"
"They don't have this," you explain, touching the pad near the door and turning up the power.

The room surges with ambient Kryptonite Energy. This was originally designed as a Cage for a Kryptonian Prisoner, but Kara told you about how her Step-Sister used it to train her to fight without her powers.

You approach Power Girl and grab her arms. She tries to resist, but finds that her fantastic strength is gone.

"You're just a powerless bondage slut in here now..."