Yaiba and his friends storm the underground empire, only to find a terrifying new threat waiting for them. The true mastermind behind it all is finally revealed as Yaiba's archenemy Onimaru once again strikes from the shadows! But Onimaru's goal is far greater than just defeating Yaiba—he wants to break the Eight Seals hidden throughout Japan to unleash a terrifying ancient demon and use its massive power to take control of the world!
