I've started a new game in Sekiro and I'm already up to Ashina Castle after roughly three-ish hours of play, where it previously took me much longer. I took down the chained ogre, General Tenzen, Juzo the Drunkard, Lady Butterfly, GYOUBU MASATAKA ONIWA, and the 420bull without deaths. I've only had a true death three times and two of them were to the ninja by the mist raven. The third death was to a spear guy who locked me in a corner.
Things I've learned since starting the new playthrough are that the Buddhist candies are actually super useful and the firecrackers can cheap out just about everyone. I don't think I got hit by Gyoubu more than once.