Last Boss, Yametemita: Shujinkou ni Taosareta Furi Shite Jiyuu ni Ikitemita

The strongest final boss in RPG history figures out a way to get super rich in his own world! Demon Lord Menas, ruler of the Noa Empire, finds the Resistance's forces on his doorstep. While Alex, a determined, beautiful, blonde young lady stands before him, he gets this weird feeling of deja vu... Isn't this just like the prologue of 'ResNoa', the video game he plays in his dreams?! Menas realizes that he was the final boss of his own world all along! He fakes his death at the hands of Alex and seizes his chance at a brand new life with both hands. Our dark hero takes his world by storm, using whatever cheat codes he has to protect his newfound freedom!

(Source: MANGA UP!)