I am working on making an RPG Game with an end of the world storyline, I want it to be like a huge asteroid is coming to hit earth. I got inspiration from an asteroid map damage simulator website, you can visit it and input the max option if you want to see what I mean. I want my RPG game to be about having to survive the fallout but I am unsure of how to make a system in which it is fun (btw its an indie game). I've got the basics down, but I am unsure how to make the game more RPG'y. Like should it be round based or what? Was looking on this website https://forums.rpgmakerweb.com/index.php?threads/100-free-to-use-game-ideas-storyline-concepts.20786/ but I couldn't find anything that resonated with me. I also want to include weapons and combat.
Simple Question: Ideas for a game that includes the end of humanity and combat
(english not my first language sry)