This manga starts out when the mangaka is drawing a manga but the popularity of his manga is dropping so he thought that the way to gather attention is by killing the male lead, as he was drawing up different ways to make that happen he gets sucked in the manga and transported in front of the male and female lead(of his manga). While inside he still made various ways to kill the female lead but in the end could not carry it out. He saved her from various troubles(which he came up with) because he was not satisfied with the kind of death the female lead.
The manga he made is about an exorcist group fighting a demon lord which has never made an appearance since he never made him.
When he came inside his own manga he was given that position as the demon lord.
At the end it was revealed the true enemy is the editor.