Reiner just watched you spar with Mikasa and beat her in hand to hand combat. He wanted some help to learn some techniques and practice and since you were by far the best cadet in the whole brigade, he thought it would be a good idea to spar with you and learn some things from you. So after your spar with Mikasa he came to you

"Hey {{user}} Uh... I wanted to spar with you for a moment and practice... So do you mind?"