The Stone Hashira

Gyorei (Gyomei)

Two creators rank Gyorei among the hardest Hashira to fight. He drops Arcs of Justice, Stone's last move, now at 10%, plus the Stone Haori, the Stone Necklace and the Stone Slayer Uniform.

He shares the Stone Sanctuary yard with the Stone trainer of the same name, the Thunder Trainee and the Stone Trainee, which is likely why one player counted four bosses there.

Gyorei in the Stone Sanctuary yard, among red posts, with his bar at the top of the screen.

Health: 3,000
Chest: World Events Chest
Per kill: 1,000 Exp, 450 Wen
When: Day and night

Up into Stone Sanctuary

The Stone Sanctuary yard of red posts, north-east of Hidden Mist Village, up the rock ledges.

Teleport to the Hidden Mist shrine.
Cross the village to the north-east.
Climb the rock ledges into Stone Sanctuary; Wall Climb helps.
Gyorei stands among the red posts, with the Thunder Trainee and Stone Trainee close by.

The in-game map with boss names switched on — Gyorei's marker on the in-game map with boss names switched on. Every marker is on the interactive map.

Arcs of Justice and the Stone gear

Item	Chance	Kills for a 90% chance
Arcs of Justice move scroll	10%5% at launch	22
Stone Haori	3%	76
Stone Necklace	5%	45
Stone Slayer Uniform	5%	45

The Stone Haori is Mythic and the Stone Necklace Legendary; their stats are on the accessories page. The Stone weapon, the Axe and Mace, is not his: it drops from the Stone Trainee in the same yard, 15% since V0.98.

Why creators call him hard

Two creators call him very hard: one says he blocks often and is one of the hardest to fight, the other that he does a ton of damage.
He uses Arcs of Justice, the very move you are farming, and one creator says it cannot be stopped.
One creator's method: lead him to a wall, then to a hole outside the fence; at a quarter of your health, climb a wall to heal and come back.
One creator strongly advises a squad, though each extra player adds 1,000 to his health.

Gyorei's health bar by day after the patch — By day, after the patch: `Arcs of Justice x1 (10%)`, struck through for this player; the other three lines unchanged.

Gyorei's health bar at launch — `The Stone Hashira` `Gyorei`: `Arcs of Justice x1 (5%)` struck with `Must be Slayer`, `Stone Haori x1 (3%)`, `Stone Necklace x1 (5%)`, `Stone Slayer Uniform x1 (5%)`.

Four bosses in one yard

I can't get Arcs of Justice.: It reads 10% now, and the 35-kill pity covers it; see the pity.
Why are there four bosses at Stone Sanctuary?: Gyorei the boss, the Stone trainer also named Gyorei, the Thunder Trainee and the Stone Trainee all stand in the same yard. Only the boss drops Arcs of Justice.

A farming method and a full fight

How To EASILY Farm Gyomei | Project Slayers 2
A wall-and-hole method for farming Gyorei with fewer deaths.

Slayers 2 Gyomei boss fight
A full daytime Gyorei fight in Stone Sanctuary.

The other Hashira

The demon side has its own bosses, starting with Gyutai; every boss is compared on the bosses page, which also has the drop odds calculator.