Saikyou Onmyouji no Isekai Tenseiki ~Geboku no Youkaidomo ni Kurabete Monster ga Yowai Sugirundaga~ - Vol. 7 Ch. 27

[DTJames]

Oh fuck what. He's actually Demon Lord? I didn't expected him to be one since he self inserted into this world that already had Hero and Demon Lord system existed in place.

THIS IS CRAZY AND HARD

 

[Gbiel984012]

it had its minor shows that he was the demon lord, first, the miasma the elf girl said he emanated, the part where spirits avoided him, and the bandit attack that the princess said to capture as most as possible to make it harder, but when he caught without a sweat she seemed down before going back to her poker face

 

[TNT261]

Okay I'll just have to do a full reread. Looks like that "MC is actually the final boss" is sprinkled throughout.