My Princess Is A Stallion

Sae Yoijima, a masculine office worker with a heightened sense of justice, is caught off guard when the handsome, muscular, and effeminate Haruchika Ego fiercely pursues her. But, Sae has a secret. In her previous life, she was a knight. Haruchika becomes Sae's chiropractor and safe haven, as he doesn't make a mockery of Sae for talking about her previous life.

One day, when Sae finds herself in a rather compromising situation, Haruchika comes to save the day. He had tried to sideline his feelings for her, but now he feels he must punish her for allowing herself to nearly fall victim! What!? Is Haruchika the princess Sae's been looking for!? Lost in a haze of confusion, when Sae comes to, she finds herself being pleasured by a man! Yet, despite the pain, something feels good about his big body being pressed against hers...!

(Source: Renta!)
Note: Chapter count includes one extra chapter.