I had this NPC harass the party throughout the adventure withdrawing before she could be cornered. They eventually pinned her at the Lake Bed (see tactics below). But she eventually became a respected enemy and instead of killing her they knocked her out and used the sacred brush to rewrite her memory and alignment. She is now a loyal guard manning the walls of the PCs castle – Ashina Castle.

The Pen of Heaven’s Door. This one-use item allows the user to read a person mind as if it was a picture book and allows the target of the pen’s story to be changed or re-written. It has the same effect of a hold person spell (which immediately ends if any physical damage is inflicted), a 9th level modify memory and compel spell with a DC 20 Charisma saving throw to resist the items changes (inspired by Jojo).

NPC is a direct Inspiration: Okami Leader Shizu from Sekiro.

OKAMI LEADER SHIZU

Medium humanoid (goblinoid, okami), neutral evil

Armor Class 14 (natural armour, ceremonial armor)

Hit Points 136 (16d8 + 64)

Speed 40 ft.

STR	DEX	CON	INT	WIS	CHA
10 (+0)	27 (+8)	14 (+4)	12 (+1)	16 (+3)	16 (+3)

Saving Throws CON +8, WIS +7, CHA +7

Skills Insight +7, Perception +7

Damage Resistances Lightning, Thunder

Damage Vulnerabilities Poison

Senses passive Perception 17

Languages Common, Goblin, Giant

Challenge 9 (5,000 XP)

Cunning Action. Shizu can take a bonus action to take the Dash, Disengage, or Hide action.

Evasion. If Shizu is subjected to an effect that allows her to make a Dexterity saving throw to take only half damage, she instead takes no damage if she succeeds on the saving throw, and only half damage if she fails.

Magic Resistance. Shizu has advantage on saving throws against spells and other magical effects

Martial Advantage. Once per turn, Shizu can deal an extra 10 (3d6) damage to a creature she hits with a weapon attack if that creature is within 5 feet of an ally of Shizu that isn’t incapacitated.

ACTIONS

Arachrist. Melee Weapon Attack: +4 to hit, reach 5ft., one target. Hit: 4 (1d8) slashing damage (see Treasure).

Lightning Kick. Shizu kicks a ball at a place she can see within 120 feet of her. As the ball travels it gathers lighting and detonates for 30 (4d10 + 8) lightning and thunder damage in a 10-foot sphere centred on this point. Targets can halve the damage on a successful DC 20 Dexterity saving throw. Anyone taking lightning or thunder damage is also stunned until the end of their next turn.

Leadership (Recharges after a Short or Long Rest). For 1 minute, Shizu can utter a special command or warning whenever a nonhostile creature that she can see within 30 feet of her makes an attack roll or a saving throw. The creature can add a d4 to its roll provided it can hear and understand her. A creature can benefit from only one Leadership die at a time. This effect ends if Shizu is incapacitated.

Treasure

ARACHRIST (“Spider Slayer”)

This mithril longsword has a cold iron hilt inset with silver runes. The pommel is decorated with a polished jasper orb. The longsword is normally +2. However, against spiders and arachnids (including giant scorpions and spider-like monsters), the sword is +3 and inflicts double damage. On a natural “to hit” roll of 20, any true spider (large, huge, giant, phase, etc.) is struck dead.

Arachrist glows with a clear white light when spiders approach within 50′. This sword allows its wielder to save at +3 versus web spells, and he or she may cut through such webs at a rate of 3′ per round. The wielder may cut through a non-magical web at twice that rate.

Arachrist is chaotic-good aligned. However, it has so long lain idle that it is presently cursed. Its wielder must engage all spiders and arachnids in sight, regardless of odds, unless he or she can successfully save versus spells. The curse remains until the sword has slain 30 hit dice worth of spiders.

And an amulet of proof against detection and location.
Imperator Syandana.