They start with an overarching theme and they plan out every single thing leading up to the comeback, during the album release and for a certain period after the album release (promotional period). Then they revisit the previous theme to tie it in with their new theme. Notice how their choreography always matches the song, telling a story and the song placements in their albums also aim to tell a story. Notice how even their stages are planned out so that it gives us little extra details.
When it comes to BTS their work is so intricately woven that you can't help but be amazed. And that is one of the things that make them stand out the most. They are the ultimate group to follow if you love mind mapping and discovering new things because they draw inspiration from multiple domains.