Knowing the Nioh 2 Darkness in the Capital Kodama locations will help anyone going through this hard expansion. And not only will it slightly ease the difficulty, it will also unlock the “Kodama Pathfinder” trophy. Nice.

Unlockable Unlocking Areas on Tokyo Hayama Castle II

You really don't have to pay attention to the guide if you take it in order (and I encourage you to treat it like one) but you will need to get all of the following Dragon Seals and unlock each Armory NPC (in order). You get every upgrade (ver 1.15) when you get each Armory (Tiers I & II).

Grand Armor Minstrel of Lord (Lv10).

Beam Powered Armour (Vers. I & II).

Corsair Greaves Armor (Vers. I).

Corsair Greaves Legs (Vers. I).

Mounted Berserker Armor (Vers. I).

Enigmatic Iron Boots (I).

Axe Thrower (I).

Havoc Buff (I).

Axe Thrower Gloves (I).

Dragon Cannon (I).

Wolf Pack Mammoth Armor (I).

Deluxe Assault Boat (I).

Ielieg Ability Armory (i.e. Milliner on subsequent playthroughs and if you've already unlocked Malevolent System / Days of Abandonic History). There are two rolls in all of this… ↑Rune Dice (All 3) x 80 = 10 Weapons DMG×2. Spears DMG×2. Bow DMG×1. All Weapons DMG ×1.5

Rune Dice (All 3) x 20 = 10 Weapons DMG×2. Spears DMG×2. Arrows DMG×3. Bow DMG×1. All Weapons DMG ×1.5

Rune Dice (All 3) x 12 = 20 Head & Back DMG×3. All Armor DMG=5. All Weapons DMG×1.5

Rune Dice (All 3) x 1 = 24 Breath DMG. Bow DMG×1. All Armour DMG×1.5

Note that the "Elemental Spell" you get from getting the Malevolent System Disc (XESN-0612) does NOT do any of the things shown here. The likely reason is that as of the last patch 2 things changed and they changed it to cast the elemental attack on the character, not you. But still it gets you the Spell.

So Kiria gets 13 Weapons DMG×2, but she only has a grab and thrown master. That means if you drop her