|“||I will trample you to death, silly Chinese Canadian baby man.||”|
Poseidon once tried to woo Demeter while she was searching for her kidnapped daughter, Persephone. She rejected his advances and transformed herself into a mare to escape him. Transforming into a stallion, the god chased her until she was tired, producing Arion and his sister Despoina as a result.
Arion is first mentioned by Hazel when she sees him in Alaska in her former life. She follows the horse around all day, trying to get close enough to it to ride it, but Arion always runs away, eventually using his incredible speed to run far away and disappear for several decades.
Arion was later caught by the Amazons (which took them many years) and caged because he couldn't be tamed by any of the members in their ranks. Queen Hylla says that Arion would only be released by the strongest female warrior, but Arion hates all the Amazons. When Hazel arrives, she pulls gold from the ground and gives it to Arion. Later, during Hazel, Percy Jackson, and Frank Zhang's escape, she sets Arion free and the latter pulls Frank and Percy in a chariot while Hazel rides on his back. He follows Hazel all the way up to Alaska and helps her in her fight against the giant Alcyoneus. He drags Alcyoneus across the border, out of Alaska and into Canada as the giant cannot die in his homeland. Arion then carries the group back to Camp Jupiter in four hours and Hazel rides him into battle against the army of the giant Polybotes, which they eventually win.
After Leo's attack on New Rome, while possessed by an eidolon, Hazel summons Arion as a distraction to the angered Romans. Hazel rides Arion out of New Rome while being chased by an angry mob, but manages to escape. The two reunite with the others in Utah where Leo tells Hazel that Arion can stay in the stables he built in the Argo II. Hazel declines and states that Arion is a free spirit. On cue, the horse runs away as Leo gives Hazel a tour of the ship. Hazel and Leo, on a search for lime and Celestial Bronze, ride Arion to the Great Salt Lake. Leo then appreciates why cars are measured in horsepower after noting Arion's amazing speed. After finding the supplies, Hazel calls Arion and the demigods flee from the crazy nymphs and Narcissus.
Arion is stated, alongside Blackjack, as a companion that hasn't been seen after the demigods continue on their perilous journey. When Hazel, Leo, and Frank are held hostage by ichthyocentaurs, Hazel is allowed to be free due to the creature's fascination with her father and Arion. Percy later states that Arion and Blackjack haven't been seen in days as they reach Rome.
Hazel spots Arion in the distance and asks Leo to land the ship close to the ground so she can speak with him. Arion then takes Hazel to a spot to meet with Hecate, goddess of magic. However, Arion becomes very nervous as he gets closer to the goddess.
Arion is ridden by Hazel during the second wave of the assault. He reluctantly carries Apollo and Meg McCaffrey to Temple Hill. When they reach Tyson and Ella at the Temple of Jupiter Optimus Maximus, he allows his half-brother to pet his snout before he zooms off to New Rome. The two fight off a horde of the undead and when Hazel learns of Frank’s actions, sends him to the Caldecott Tunnel to find him. He succeeds and returns the son of Mars alive.
Arion is highly confident and proud, not taking criticism well, and has a distinct independent streak. He particularly exhibits notably profane language. Despite his faults, he is very loyal to Hazel whom he chose to be his rider. Before Hazel claimed him, no one could touch him. The horse has an extremely foul mouth, according to Percy when translating the horse's language.
|“||...Arion runs like the wind over land and sea.||”|
- Enhanced Speed: He can run eight hundred miles per hour, traveling faster than sound at sea level and in dry air which is approximately 768 miles per hour depending on conditions. He's also one of the fastest beings in existence.
- Sonic Blasts: He can create sonic blasts when traveling at super speed, probably due to breaking the sound barrier.
- Enhanced Walk: He can run on vertical slopes and on water without sinking.
- Enhanced Strength: He possesses superhuman strength. Arion is strong enough to easily drag beings as large as Alcyoneus for more than ten miles.
- He can make incredible leaps across long distances. He once jumped over a 50 ft. chasm.
- Enhanced Physiology: Arion can consume substances the normal horses, and most creatures in general, cannot eat, such as chunks of solid gold.
According to Hylla, there is a prophecy stating that the most courageous female warrior would someday master Arion and ride him to victory, ushering in a new era of prosperity for the Amazons. The exact lines of this prophecy remain unknown. This might have come to pass since Hazel mastered Arion and now the Amazons are working with Camp Jupiter instead of against them.
- When riding Arion, Hazel did not feel as if she was going to fall off the horse or fly backward, but Percy and Frank in the chariot felt the backward pull from the speed they were going and almost fell off.
- Arion is a cavalry horse, not a chariot/wagon pulling horse.
- Arion happens to curse a lot. However, Percy leaves out the curse words when translating what Arion is saying to people.
- Arion is commonly rude, as he called Frank a Chinese-Canadian baby man and that he was going to trample Frank to death.
- Arion can eat food normally preferred by horses, but he prefers lumps of gold.
- Both of his sisters, Persephone and Despoina, are goddesses of seasons (spring and winter respectively). It is possible that if Arion had been born a "normal god" (i.e., with a humanoid form), he could have been the god of summer or autumn.
- Curiously, even being a son of Poseidon and Demeter he doesn't has any apparently feature of his both parents what could be justificaded because that he is a divine-horse or just because godly genetic doesn't work like the mortal.
- Although he has caramel fur, this could be the mix of Poseidon's jet black hair and the Demeter's blonde hair, as his mane is as black as Poseidon's hair and his eyes are brown like Demeter's eyes.
- Although he can walk both in vertical-land and water, this could be explained by his parents powers.
- The reason for him being able to run up in vertical slopes can either be because runs fast enough to not fall or because of his mother, Demeter, as he hasn't been shown vertical-running in another surperficeis that not are earth-like. And the reason for how he can run up on water without sinking can either be because he runs fast enough to keep from sinking into the water or because of his father, Poseidon.
- It's possible that Arion is as strong as a god and he's also immortal as his parents are both two very powerful gods (Demeter and Poseidon respectively).