How to trigger Emma fight in Sekiro?

Could you elaborate on the steps needed to initiate the Emma fight in Sekiro: Shadows Die Twice? Are there any prerequisites or specific actions that must be taken to trigger this confrontation? Are there any hidden or non-obvious methods that players might overlook? Additionally, are there any consequences or rewards associated with completing this fight? It would be greatly appreciated if you could provide a detailed and comprehensive breakdown of the process to help players navigate this aspect of the game.