Fujimi Tensei: Kuzu da Kedo Saisei Chi to de Muso Shimasu, chapter 3
https://comic-top.com/fujimi-tensei-kuzu-da-kedo-saisei-chi-to-de-muso-shimasu-chapter-3-1/

Dominatrix demoness with blood-sucking thorny rose vines that come out of her vagina restrains the masochist protagonist and some damsels until he tricks her into beheading him and triggering his regeneration powers.
His headless body becomes self aware, muscular and penetrates the villainess with a punch when she's trying to avoid him. She sticks her tongue out and spreads her legs to show off her labia and buttocks before collapsing on the ground.