Looks like there's a major issue with Katana ZERO due to an update that was pushed live early. This update can corrupt your save file if you're not careful. The best option is to simply not play the game until the fix is live. Check out the full details on this issue below.
Please don't update Katana ZERO on Switch. This update is not supposed to be live yet and it will corrupt your save file. This will be fixed immediately. Clarification - updating the game will not delete your save. If you boot the updated version, the game will say that your save file is corrupted and ask if you want to reset it. If you don't reset it, then you'll be fine.