I just had this isekai idea just pop into my brain. Where the story starts off in our Japanese protagonist from the modern age dying then waking up in a pre-medieval world of magic and swords. each chapter is one point of their life and the story arc ends when that character dies. their descendant(s) talk about how he changed things for the best or worst.
2 decades later, another Isekai protagonist appears. maybe they're Indian, Chinese, or whatever country it is, they are from from the same time period as the previous guy and time on earth only passed by about a year and 1 day since the previous protagonist. a new circle of change happens in a span of their lifetime. the current protagonist meets the descendants of the previous and either marry or are well known friends.
Again, adventure, death, 2 decade wait, new guy (or gal) shows up, repeat.
this goes on and on until this world matches the current technological advancement of earth. they are somehow able to connect to earth through magic, as they tracked the origin of some historical Isekai protagonist, and discover the "heavens (or hell) that these important figures come from
Idk, some random thought I had