The Idaten Deities Know Only Peace Vol. 4 (manga)

Long ago, demonkind was sealed away after a fierce battle. Eight hundred years later, the Idaten, softened by centuries of peace, are attacked once again by demons! But the clash results in another resounding victory for the Idaten. With the demons facing a despairingly large disparity in strength, it is only a matter of time before they are annihilated...

unless Miku can turn things around with her remarkable powers! The strongest Idaten's secret will soon be revealed, along with the true identity of the mysterious Demon Lord! Who will triumph - gods or demons?!