Slot IDs matter
Each character stores its own slot number, and the game saves back to the file with
that number. If two characters share a slot, playing one overwrites the other.
Pick an unused number, ideally 1–9. The file is named to match (slot 6 → Save0006.sav).
Where saves live
PC (Steam):
Documents\My Games\Borderlands 2\WillowGame\SaveData\<Steam ID>\
If Steam Cloud reports a conflict on the next launch, choose the local files.
Profiles (profile.bin / Player1) hold badass rank, golden keys and
settings. Replacing one overwrites that device's progress.