Foolish Saintess Finds the Second Life Unfamiliar

Isabel, the only comic relief character in the grimdark fantasy ‘An Old Tale’, is sent back in time—just before the Demon King brings about the world’s destruction.
Kim Su-min, the sole reader of ‘An Old Tale’, suddenly finds himself possessing Isabel’s guardian angel.
“Isabel, the first thing you should do after regressing is make a plan.”
“I see! But… what exactly is regression?”
…Is the second life always this exhausting?