I'd say the stamina bar is obsolete or should be reworked entirely. I think the main issue is It just doesn't make sense to have blocking use up stamina. Imagine Sekiro but you had to walk away from the boss after 25 seconds (or just stand there waiting for the refill while getting hit, as did I).
I would scrap it entirely and maybe weaken normal attacks a tiny bit (while giving him less defense after his posture is broken).
But if you wanna keep in some stamina management maybe deflecting attacks could fill it up faster.
Otherwise this is a really solid project. The bosses might be bit too fast (or that's just me not having played sekiro in ages) and have too little attacks, but what they got is solid. I especially like the wandering kings teleportation, might need some tweaking so you can properly react to him appearing behind you (which I think needs you turning around which made me mess up), but other than that I am a huge fan of any and all teleportation shenanigans.