https://www.cmoa.jp/title/253380/

"I can’t believe my virginity is being taken like this――!” Momo, a former track athlete, can no longer run due to an injury she sustained during her career. While her treatments aren’t progressing, Dr. Dan encourages her, saying, “Let’s overcome this together.” Moved by his strong words, Momo begins to trust him, only to later discover that Dan is actually the underboss of a yakuza gang controlling the underground world! As soon as she learns his secret, he reveals his true nature, saying, “After treatment, I need women to calm myself down.” What she thought was a one-night fling turns into being loved deeply and passionately every day ― in ways she never imagined!