바탕, 토대, 기반, 기초 what's the difference?
I think they can all mean a literal or figurative foundation for something. Whether it's an idea, a theme for a party or a physical foundation for a house or other project.
바탕, 토대 and 기초 can all be used with 을/를 두다 to mean 'based on a true story.' or 'based on a comic book' etc. While 기반을 둔 can be used to say based on evidence or research but I don't think it would be used with anything fictional.