Ruin is the fifth member of the Ancients to reveal herself. She serves as her master's hunter and assassin.
Ruin wears straps decorated with fishbone on her ankles and feet, a black skirt with golden lace around the top, a seashell bra, a long shawl of black cloth with the Ancient's mark on the back, that being a white segmented diamond insignia atop a black base, and a black medallion that also bears the emblem of the Ancient's on it. As a nixie she has webbed toes, aqua colored scales on her thighs, lower arms, chest, and her long reptilian tail. She has earfins, long teal colored hair, and eyes made of gray ancient metal with violet irises and glowing white rings around them. She carries a trident made of ancient metal, its silvery steel having glowing etchings of white light throughout it.
Ruin has a very focused demeanor with shades of tranquility and arrogance mixed in. She's very calm and self-assured in her abilities, precise and graceful with her movements, and also cruel and heartless with those she comes across. She sees herself first and foremost as her master's "pet" and wishes for nothing more than to grant him anything he desires. Although she's a nixie, she acts more like an attack dog for her master, hunting down his targets with silent ferocity in hopes to please the one she loves. She prefers to strike with the element of surprise and advantage on her side, although once she's seen she has no qualms with openly attacking her prey without any fear or hesitation.
Aquakinesis: Like Specca, Ruin is able to control water she comes into contact with. Unlike Specca, however, Ruin is able to do so with greater ease and effect. Whenever she's standing in or around water, it always appears to flow with and around her, almost following her without any effort on her part. When she uses the water to attack or repel her opponents, she's able to summon forth powerful waves and explosions of it nearly instantly that can knock back even a minotaur.
Strength: Nixie's aren't renowned for their physical strength, but Ruin is clearly a big exception to that. Being able to block fierce attacks from a minotaur without even batting an eyelash or budging an inch shows very clearly how strong this woman is.
Magic: It's unknown if Ruin is able to charm her prey given the status of her eyes, however she has demonstrated a high proficiency for using magic other than water or charming based spells. Using her trident she's able to create deadly bursts of raw magical energy to attack and obliterate her foes.
Ancient Eyes: Ruin's eyes aren't normal in any regard. They are said to be made of steel with violet irises in them yet move and act like normal eyes do. She's able to see perfectly on land without the need for glasses, and likely has other enhancements to her sight that haven't been revealed yet.
The Ancient Nixie
As explained by Minos in S2. Act I, Ruin and her fellow disciples are not just powerful and dangerous monsters, they were the first of their respective races to come into existence. Although it isn't clear yet as to how this came to be, it seems Ruin was the first nixie to exist in the world, and wasn't born by normal means. What that entails and how it came to be has yet to be revealed.
As an Ancient, Ruin is gifted not only with supernatural magic and strength, she is also able to be revived by her master should she ever die. Though it has been stated it takes about a century for an Ancient to be resurrected after their death, she is able to effectively come back from the dead as many times as her master wishes. This also plays into how Aeon is unable to perceive her or the other Ancients' actions in the timeline. As an Ancient who is more or less unbound by the laws of life and death, Ruin has no timeline of her own that she follows, thus her actions in the world are shrouded in mystery even for the Dark Queen of Time.
However there does appear to be a way to permanently scar the Ancients. As described by Minos, this involves burning an Ancient's body part in ceremonial fire to completely destroy it. Should this happen, when the Ancient is revived by their master, the part of their body burned away by that fire isn't able to be regenerated, and instead the Ancient is reborn with a prosthetic of ancient metal and magic.
It hasn't been made known yet how it occurred, but at some point in history Ruin lost her eyes to the minotaurs who then burned them in a ritualistic fire to permanently destroy them. After being reborn again, Ruin was given prosthetic eyes by her master.