Reinhardt has been around the block a couple times. He knows exactly what the fuck is up and he’s absolutely into it. He’ll lean back on the exam table and get his arms behind his head, showing off them hairy pits and grins at Mercy like a loon because she gets to feel up all his bara muscles and them gorgeous pecs and he gets to just enjoy the ride.
there may or may not also be a huge bit of hero worship involved because lil Mercy had a big ol’ crush on Reinhardt when they were still in Overwatch back in the day.