The hero meet demon lord and want to fight him

the demon lord then say human are not that "innoncent"

and tell the hero say demon are evil, say there are prime minister who become corrupted and become evil and he then make the country into chaos

the demon lord then say the prime minister was a pervert and he collecting many beautiful princess around many country to make harem but it fail.

then he purposely throw the country into chaos and say he was possesed by the demon even thought it was a lie

and the hero in the end follow the demon lord.

i always think it was maoyuu-maou-yuusha-kono-watashi-no-mono-tonare-yuusha-yo-kotowaru

but there are many version on it and i never see the harem princess part

i think it was a different manga with nearly same plot line like yuusha but this manga i read was kinda more a comedy gag manga than yuusha maou manga which was kinda serious based.