Castle of Stone

Castle of Stone is a Guardian skill.

Description
This is a special defensive skill available only to Guardians. Once the spell is cast, the user is surrounded by a yellow light and is invulnerable to attacks (does not take damage). However, he is also completely immobilized for the duration of the skill. This spell only lasts for ten seconds, and because its cooldown time is ten minutes, it is generally viewed as an emergency defensive measure that can only be used once in a particular battle.

Saving Serara arc
After Demiqas orders the Brigandia men to assist in his fight against Nyanta, Naotsugu intervenes, using Anchor Howl to attract their attention and preventing them from helping their guild master. He uses Castle of Stone to both negate the damage being dealt to them and to hide Shiroe and Nyanta's strategy.

Gold of the Kunie arc
When the Abyssal Shaft Raid Party goes up against Ruseato of Seven Prison a second time, Naotsugu takes the first hit alone, using Castle of Stone to negate the damage. After they escape to the Great Hall, it is revealed that Dinclon, the raid party's other Guardian, was reserving his Castle of Stone to take Tarutauruga of Fourth Prison's first attack while the other half of the raid party took on Ibura Habura of Third Prison.

Nightingale's Song arc
When the Genius Eirenus invades Akiba, it sucks all the city's Adventurers into a Level 65 raid dungeon based on the city. It then abuses the Teacher System to reduce all veteran Adventurers' levels to 35, which affects such Guardians as Naotsugu and Dinclon. When Naotsugu and Dinclon's respective parties meet after kiting different enemies, they use the Scissors tactic to trade their respective Level 65 Raid-ranked foes. Per Rieze's plan, the two Guardians use Castle of Stone so that the two now-Level 35 Guardians can tank against their targets despite the massive level disadvantage, allowing their other party members to beat these enemies and win this skirmish.