Have you been checking out the DLC offerings for Fire Emblem yet? In a nutshell, after progressing a bit in the story, you can access the DLC store to buy new maps that can offer new characters, items, and other perks. As a reminder, Champions of Yore 1 is still free until March 6th.
This new video will show off all of the DLC on offer outside of Japan in the near future as part of the first wave of content, as well as a tiny overview of the overarching story and a layout of most of the maps. Not everything is out yet, but Nintendo is updating the store on a consistent basis for Season 1.
As a recap, here's everything you can get in Season 1, when it all sees an eventual release: