This Starts out with a grandson who visited His Grandparents that had recently died and went to clean their belongings.

One day and he discovers a diary which was written by her grandma that tells of a secret adventure with Grandpa which both of them had disappeared for a day and returned in the next day.

It was written with two sides which corresponds to their side of their stories.

Both of them were summoned as heroes and were reverted back to their youths and had to set out and defeat the demon king.

Most of which Grandma complaining that Grandpa was always gathers girls while Grandpa was mostly scared that Grandma was gonna get taken away by Handsome and young attractive men.