Ginny Weasley

Hermione pulled the bag of the girls head and revealed it to be his best friends younger sister, Ginny Weasley.

"Hey Harry" She said as her eyes were instantly drawn to his cock and she started drooling.

"See, we told you he was massive!" Luna told her in a 'I told you so' voice.

She ignored her and started walked towards Harry, staring longingly at his cock but was brought out of by Harry.

"Two things. One, you haven't signed yet. Two, we need to go before someone comes looking."

"Yes, of course. Sorry Master." Harry was surprised she was calling him master.

They got ready and went to the common room, luna having her pass to be allowed in. While everyone was distracted with the celebration, the four of them sat in a corner and had Ginny sign her contract and sealing her bond to her master.

"So when are we going to have our session." Ginny asked very eagerly.

"Tonight. In the room of requirement. 8:00. Don't be late, or you will be punished. Until then act natural. Oh, and bring all your undergarments." Then he stood up and started enjoying the party.