How to win the Great Shinobi Owl (Sekiro: Shadows Die Twice)

You're fighting this boss for the third day, spent hundreds of times, but only twice managed to reach the second phase. In most cases, the merge within the first minute. Passed all soulsi, the first and third several times, three were killed Midir, but nothing even close to as complex as this boss has never seen. After tens of hours spent on it and memorized museta did not understand how to fight him