The Red Stone of Aja (in Japanese: エイジャの赤石, Eija no Sekiseki) is a perfect gemstone, without a single flaw, capable of refracting light thousands of times in a single point, generating a powerful light beam. It is a recurring object featured in Jojo's Bizarre Adventure.
This stone was seek by the Pillar Men, ancient super beings, who |wanted it to use in conjunction with the Stone Mask so they would overcome their weakness to sunlight and become the ultimate life form. They searched the Red Stone for centuries, but the Hamon Clan, the only ones who could match the Pillar Men due to their breathing technique that generates energy similar to the sunlight, get hold of the stone first and put the Pillar Men into hibernation. They never destroyed the Red Stone, but instead secured it, because of a prophecy that told that destroying the stone would make defeating the Pillar Men even more difficult.
By the time of the Second World War, the Pillar Men woke up and resumed their search. The stone was being held by Lisa Lisa, the last master of the Hamon, who taught Joseph Joestar so he could defeat the Pillar Men. Cars, the leader of the Pillar Men, finally gets hold of the stone with his treachery, using it with the Stone Mask and becoming the ultimate life form. However, Joseph Joestar uses a concentrated Ripple Overdrive in the stone, making a volcano explode and sending Cars into space.
- This object's name "Aja" is in reference to Steely Dan's most popular album "Aja". It could also be referencing the British progressive rock band called Asia.
- Aja was literally pronounced as "Asia".
- It is sometimes called the "Red Stone".
- It is also known as "Super Aja" (in Japanese: スパーエイジャ, Supā Eija).
- In Touhou Project, a Spell Card called New Impossible Request "Red Stone of Aja" referencing the mystic stone of the same name.
- In the 18th chapter of Part VIII: JoJolion, a gem seen on a little girl's compact has a similar appearance to the Stone.
- As one of the most famous items of the Jojo's Bizarre Adventure franchise, the Red Stone of Aja has appeared in several Jojo's Bizarre Adventure games.
- It appears as one of Young Joseph's super moves in "JoJo's Bizarre Adventure: Heritage for the Future".
- It appears as the main collectable item in one mission of Jojo's Bizarre Adventure World in Jump Ultimate Stars.
- It appears as both Lisa Lisa's HHA (similar to Joseph's special move in Heritage for the Future) and the item that allows Pillar Men and Vampire characters to fight on stages that contain sunlight.
- It appears as Joseph's Ultimate Hero Burst in J-Star Victory Vs as he uses it in the same way seen in the Capcom fighting game.