Urotsukidoji: Legend of the Overfiend, Volume 4

The skies are darkening, the air becoming thick and the final days of life on earth are about to count down. The Overfiend is about to be reborn on earth and both beast and demon realms are looking to take full advantage and use this to take over.

After surviving his last encounter, Nagumo isn't acting like himself. Becoming more bold and confident, possibly blinded by the pleasure and power of the Overfiend, Nagumo submits to the ecstasy and becomes the Overfiend.