The hero Oura arrived at an old castle on his journey to defeat the demon king. By chance, he discovered an ancient super-weapon called the ‘hero cannon’ (yuusha-hou), which only activates after having sex with girls! Together with the failure succubus Tina, envious osananajimi and healer Flare, overly serious royal knight Mira, and selfish magician Ekuri, Oura’s ecchi battle begins!