searching for manhwa - transmigration

i dont know why im searching for this, i think its boring but i want to re- read.

its a manhwa transmigration into a magic/academy/not really advance/ eaurope style world.

mc died wwhile writing a boring novel and he got punished by reliving one of his completed novel. all the novel he wrote have bad endings so he choose the one with a good ending where everyone lives.
he got what he wanted but he as transmigrated as one of the many mob chracters that will die. the son of the demon lord.

he pretended to be a normal person and accidentally rescued a princess who was supposed to die in the story thuf the course of the novel changed.

he meets 3 of his subordinates and he gets transferred to an academy to gain knowledge and power so they can "rebuild" the demon empire.