|“||Good-bye, Hazel Levesque. If we both die tonight - well, I'm glad I met you.||”|
Hylla Ramírez-Arellano is a Roman demigod daughter of Bellona and Julian Ramírez-Arellano, and is Reyna Avila Ramírez-Arellano's older sister. She used to be a secretary on Circe's island, but is now the Queen of the Amazons.
She was born in Puerto Rico, as a demigod daughter of Bellona . Hylla wanted to protect her sister Reyna from violence and went to Circe's Island so that they would be safe. She became an attendant of Circe and was quite loyal to her. Then Percy Jackson and Annabeth Chase came to the island and Annabeth released Blackbeard and his pirates, who burned down the spa and took Hylla and Reyna captive. However, as daughters of Bellona, they were natural weapons experts and learned to fight quickly. Eventually, the pirates learned to respect the sisters and they later parted ways.
Hylla greets Percy Jackson and Annabeth Chase at the docks of C.C.'s Spa and Resort. She's seen holding a clipboard and asks them if it was their first time at the spa. She then takes Annabeth away for a "makeover" while Percy goes with Circe.
Hylla became the Queen of the Amazons sometime after her confrontation with Percy and Annabeth. She still has a desire to kill Percy for destroying her "home", and she reveals to Percy that she's been seeking revenge on him for the past four years. It is also revealed that Reyna is her sister. When Hazel Levesque, Percy, and Frank Zhang arrive at the Amazon base, Hylla has Percy, as well as Frank, locked up and holds a conversation with Hazel and Kinzie. Hylla also says that she knows there are both Roman and Greek demigods, but treats it as if it as nothing. She tells Hazel that Otrera, the first Amazon queen, was brought back to life due to the Doors of Death being open and that she is gaining support from some of the Amazons. Otrera plans to challenge Hylla to a battle to the death for control of the Amazons as anyone can challenge the queen for their position. While the challenge is a battle to the death, Otrera can't die and would reform everyday until she wins, making Hylla worry that she would be killed and the Amazons would follow Otrera into battle against Camp Jupiter, but Hylla would like nothing more than to help as her sister, Reyna, the praetor of Camp Jupiter.
Hylla, when learning that the trio are on a quest to free Thanatos, tells Hazel that she can't set her friends free as it would look like she was weak, but if they managed to escape somehow and defeat the Amazons loyal to Otrera, they could escape on Arion, a horse none of the Amazons could tame, but took a liking to Hazel after she had fed him a gold brick. She tells Hazel that she will hold out against Otrera as long as she can until they finish their quest and would help her sister if she survived.
During the battle at Camp Jupiter, when the forces of the two armies were almost even, the Amazons appear blowing their horns ready for battle, much to Polybotes' delight until he notices that Hylla had managed to kill Otrera two nights in a row, leading to the Amazons referring to her as "Hylla Twice-Kill." Hylla leads her warriors into battle and helps push the Giant Army into a retreat. During the celebration after the battle, she spends time with her sister. The following day, during the council meeting, she sides with Percy about letting the Greeks land after he makes a comment saying that no one had expected the Romans and Amazons to work together a week ago, saying "He's got a point!"
Hylla purposely sets Reyna, Coach Hedge, and Nico off course, pulling them to San Juan. She abducts Reyna and brings her to the Amazon's and Hunters of Artemis' base. She explains that Orion is hunting Reyna and she plans to lure him to their base. Unexpectedly, Orion kills all of their guards and invades the base. Reyna and Hylla battle Orion, but Reyna is forced to leave the battle to the Amazons and Hunters, as she must leave with Coach Hedge and Nico.
It is later revealed that Hylla survived.
Hylla is a strong and brave young woman. She loves and cares about her younger sister, Reyna. She wanted to protect Reyna, so they went to Circe's island hoping to keep her safe. She is also somewhat vengeful, and was still furious with Percy for destroying Circe's Spa, her past home, even after meeting him four years later.
In The Sea of Monsters, Hylla is described as looking like a flight attendant, according to Percy, wearing a blue business suit, with perfect makeup, her black hair pulled back in a ponytail, and a dazzling smile on her face.
Hylla is described in The Son of Neptune to look like an older version of her sister, Reyna, but was so similar in appearance to her that she could be mistaken for Reyna's twin with long black hair and dark eyes. According to Hazel, she's athletic and lean, dressed in a sleek black leather jumpsuit with Queen Hippolyta's belt, a strange-looking accessory made of interlocking gold links, around her waist. After her confrontation with Percy, Frank, and Hazel, she wears her sister's ring. As revealed in The Blood of Olympus, the most significant difference in appearance between Hylla and Reyna is the former's long white scar on her forehead, which she had received from a duel while on Blackbeard's pirate ship. The scar had faded during the last several years, to the point that anyone who didn’t know better might mistake it for a worry line.
- ADHD: Like most demigods, she possesses inborn supernatural battle reflexes and senses that she uses to analyze the fighting style of her opponent.
- Enhanced Reflexes: She showed her agility when intercepting and slashing Orion's arrow shot to Reyna.
- Dyslexia: She may be dyslexic, which makes her brain "hardwired" for Latin instead of modern languages.
- Fighting Skills: As a daughter of Bellona and the Queen of the Amazons, Hylla is undoubtedly a powerful fighter. She single-handedly defeated Otrera, the first Amazon Queen and the daughter of Ares, in two occasions. She is said to be very proficient in fighting with her dagger.
- Spanish: Hylla can fluently converse in Spanish, being Puerto Rican by birth.
- Telumkinesis: As a daughter of Bellona, Hylla is a natural weapons expert, understanding how to use weapons faster than most other demigods, and may have magical control over them.
- Hylla is called by name in The Sea of Monsters.
- In The Son of Neptune, Hylla reveals that she had a favorite pet leopard when she worked for Circe.
- Hylla has the longest gap between the time she was first introduced and the next time she appears in the series, as she appeared in The Sea of Monsters, but didn't appear again until The Son of Neptune, a five book gap. The only other character with a similar gap is Small Bob, from The Titan's Curse to The House of Hades.
- She is the first Roman demigod to appear in either of the Camp Half-Blood series, appearing in book two of the Percy Jackson and the Olympians series, making Jason Grace the second Roman to appear in the Camp Half-Blood universe.
- In The House of Hades, Hylla and Reyna are revealed to be Puerto Rican.
- Hylla is called "Hylla Twice-Kill" by the Amazons for defeating Otrera twice in a row.
- As mentioned by Reyna in The Blood of Olympus, Hylla is currently twenty two years old.