I don't know if I keep skimming over it but is there minimum recommended number of players. Could it realistically work for two players to have a campaign?
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A one on one game is totally doable, with the note that you'd have to make some decisions about Bonds and Band Sentences--both of which are designed to tie player characters (and their players) together. Either house rule that those can operate with NPCs or else the GM should account for the fact that the PC does not have their full toolbox available to them.