For example, the reason for the apocalyptic event could be a virus outbreak-pandemic that kills the majority of the world population (maybe bioweapon that backfires on the creators or sth else) or a climate change. However, I am not looking for an extraterrestrial or zombie threat.
Furthermore, I would like the story to take place 1 year after or even some time after no problem on that. I would like the story to be about world-building or civilization building like going back to a renaissance or late medieval society, technology wise. I accept that a grace period of a year or two of modern means weapons and medicine is acceptable in order to bring People equipment and start rebuilding in place with fertile agricultural land. However after a period of a few months to a year, any food supplies (canned or stored grain), weapons, fuel, and medicine Will expire or spoil, so the survivors can use them as Base equipment to build their Base or Village and fortify it, but then they Will have to start using older weapons and tools (blacksmithing).
I am not strict to medieval or renaissance, it could be even the era of the American civil war too, with early gunpowder use like muskets or the first cartridge rifles. However, I would find it easier to start with longbows, crossbows, and some sort of armor.
I don't think there is a need for an alien or fantastic threat, as human nature can be an enemy for itself, like territorial disputes, greed even abducting women (if the ratio of man to woman is large, say more women survived the event for some reason). Also an organization of such a society based on meritocracy and skills, like a mix between modern or before the event tenets with a society of 18th, 15th or 14th-century model that can work in a world of agricultural revolution and the early stages of the industrial.
I don't have a problem with recommendations for using modern technology, However, I believe that after a period of saying generously 5 years it won't be realistic. ( fuels won't Last or medicine and probably food, weapons are not sure, However, bullets do have expiring dates.
Please give any recommendations and comments. Recently I reread a similar story by FantasyLover. However, I don't remember any older stories. The last few months I spent reading fanfiction after a recommendation from here on a particular genre I like.
No problem with the amount of sex, on the condition that it doesn't expose the plot. Sex with the plot is nice as it braks tension but sex with no plot is not nice.