Stone Masks (石仮面 Ishi Kamen) are powerful ancient artifacts featured in the first two parts of JoJo's Bizarre Adventure, Phantom Blood and Battle Tendency. They are originally introduced as sacrificial devices used by certain vampiric Aztec cults.
In Battle Tendency, it is revealed that the Stone Masks were designed by Kars in an attempt to grant his race the ability to withstand sunlight; this wish is fulfilled when Kars eventually uses the Red Stone of Aja in combination with a modified Stone Mask, turning him into the Ultimate Life Form.
The conventional Stone Mask has the appearance of a somewhat-masculine face, its eye holes sharp and somewhat slanted. It has a small mouth in either a neutral position or a slight smile, with full lips and small fangs resting on the bottom lip. A ridge emerges from the bottom of the forehead, running vertically to the Mask's top, joining with another ridge extending into a spiral resting on the left of its forehead. Stone Masks commonly exhibit cracks and other signs of wear, likely due to their age. When activated, stone tendrils shoot out of fifteen holes in the mask.
The Stone Mask owned by George Joestar I bears four short lines of writing on the reverse side of the forehead. Written in an obscure, semi-cursive script, the writing and its significance remain unexplained.
Kars' modified Stone Mask has a raised depression in the middle of its forehead, in the mold of the Red Stone of Aja.
Between the 12th and 16th centuries, an ancient Aztec ritual took place in Mexico, where a man wearing a Stone Mask sacrificed a young woman and became a vampire. The man's tribe tried to conquer the world with the help of the Stone Mask and its powers, only to suddenly disappear from history.
During the mid-to-late 19th century, one Stone Mask was excavated from an Aztec ruin by a team led by Will Anthonio Zeppeli's father. After donning the mask, Zeppeli's father slaughtered his crew. While chasing down his own son to suck his blood, he died from exposure to the sun, leaving the mask to drift off into the unknown.
The same mask is eventually purchased from a London art dealer by an English aristocrat, Mary Joestar. After her death in a carriage accident, the mask is retrieved by her husband, George Joestar I, who mounts it on a wall in his family home.
During a fight between Jonathan Joestar and Dio Brando, Dio's blood spills onto the mask, causing it to activate and push itself off the wall. Though Jonathan believes only he saw it, it is later revealed that Dio witnessed the mask's activation as well.
The Mask later becomes the subject of Jonathan's research; Jonathan comes close to understanding its purpose, but his reluctance to test the mask on a human renders its secret a mystery to him. When Jonathan leaves the mansion to track down Dio's poison seller, Dio steals the mask, believing it to be an execution device that he could use on Jonathan. After testing it on a vagrant, he realizes the mask's true purpose, reclaiming the mask after the vagrant's death by sunlight.
Though Dio initially plans to kill Jonathan with a knife, Robert E. O. Speedwagon arrives with the poison seller and a police squadron. Outnumbered and surrounded, Dio announces his intention to transcend humanity. Dio attempts to stab Jonathan, but George takes the blow; nonetheless, his blood activates the mask, turning Dio into a vampire. The mask remains in Dio's possession, despite Wang Chan's short-lived attempt to salvage and sell it after the Joestar Mansion's destruction. When Dio takes refuge in an abandoned castle near Windknight's Lot, the mask is seen hanging upon one of the walls of the castle. After Dio's apparent death, Jonathan's group finds the mask, and Speedwagon smashes it to pieces with a sledgehammer.
A collection of Stone Masks surround both sites of the Pillar Men's slumber: the cave housing Santana in Mexico, and the underground ruins housing Wamuu, Esidisi and Kars in Rome. Kars later uses his collection of Stone Masks to turn humans and even horses into his own vampire servants.
It is revealed that Kars is the original creator of the Stone Masks. Though he intended to use them to give himself and his race the ability to withstand sunlight, he discovered that the mask's tendrils were unable to push their brains far enough due to their immortal bodies. Theorizing that he required greater power to strengthen the Mask, he designed a modified version meant to be combined with the Red Stone of Aja. Kars keeps this modified mask with him during his long search for the Red Stone, eventually succeeding in combining the artifacts and becoming the Ultimate Life Form. The mask is destroyed during Kars' transformation.
The Sezione Droghe decides to retrieve a Stone Mask found in an old Nazi bunker to power up Massimo Volpe. Giorno Giovanna orders Cannolo Murolo to destroy it as part of Passione's agreement with the Speedwagon Foundation, and Murolo succeeds in doing so.
The Stone Mask is activated when it is touched by blood. Once activated, the mask extends stone tendrils from its edges, piercing the wearer's skull and brain. The tendrils are meant to trigger certain precise points in the brain; the process is described as being similar to acupuncture. The process also produces a brief flash of light.
The mask's effects on the brain activate immediately upon piercing it and free the wearer from the constraints of natural limitation, causing them to gain immense strength and other abilities. This process has been shown to work on both horses and humans.
According to Robert E. O. Speedwagon, humans affected by the mask can jump five to eight meters, punch with a 2000–4000 kg/cm2 force, and triple their leg strength. However, the body is unable to adapt to this power, rendering it "dead" (in a sense) and weak to direct sunlight or the Ripple. In addition, the wearer also develops an uncontrollable bloodlust capable of overriding even familial bonds. This set of effects designates the wearer as a vampire.
Pillar Men who wear the mask are given near-invincibility and the ability to manipulate their bodies, but require even more energy from other living creatures to sustain themselves. In this augmented form, Kars was able to wipe out his entire clan.
To unlock further power, Kars created a modified Stone Mask which, when fitted with the Red Stone of Aja, has the ability to pierce a Pillar Man's skull completely. This Mask is triggered by exposure to intense light such as the UV beams released by the Nazis' anti-vampire weaponry.
The combination of the mask and the Red Stone grants a Pillar Man complete immunity to the Sun, the ability to use the Ripple, and the power to transform their bodies on a cellular level into any creature, preexisting or new. The mask itself is destroyed in the process, likely due to the immense amount of power emitted by the Red Stone.
It is unknown what would occur if a human or a vampire were to wear the Red Stone-enhanced Stone Mask.
- The third extra chapter of Steel Ball Run suggests that Stone Masks are a possible method of eventually obtaining a Stand.
- As one of the most famous items in the series, the Stone Mask has appeared in several games:
- In Heritage for the Future, when one of the players has their Guard Gauge depleted by the opponent, the Stone Mask briefly appears on the screen as part of the resulting "Stand Crash".
- In the Phantom Blood PS2 game, the Stone Mask is seen activating on-screen at the start of every battle, in addition to its regular appearances during the original story. It also appears as part of the game's loading screen.
- In All Star Battle, the mask represents the Phantom Blood arc in several trailers and in Story Mode.
- Various games in the Castlevania series have an item called a Stone Mask (sometimes called a Jade Mask), which, according to in-game descriptions, were once used in ancient rituals. Appropriately, vampires are a central element of the Castlevania universe.