The Battle of Saigagake is the last mission of Act 1 in Nioh 3, where you will take down Takeda Shingen for the second time ...
You'll need to find Tier 1 Treasure Chests in Abyss to complete specific quests. Not only will they help you with quest ...
Nioh 3 is a complex, mechanically-dense game. Let these tips help you navigate through its many systems. Or at least, refresh your memory.