Marin has ginger hair, a white sash at her waist, a black t-shirt beneath her Cloth, red leggings and a silver mask concealing her face. She also wears a black glove on her right hand.
Marin is a very straightforward woman who won't hesitate to attack, even if the opponent is a lot stronger than herself. She cares deeply for her student Seiya, and will protect him with everything she's got.
Marin is given responsibility to train Seiya for the next 7 years, as Seiya came to obtain the Pegasus Cloth and bring it back to Japan.
As his trainer, Marin makes him train hard, telling him crying won't help him fulfill his training. When Seiya defeats Cassios 7 years later and obtains the Pegasus Cloth, the victory is short as Shaina pursues Seiya in order to avenge Cassios' defeat.
Telling Seiya that he will have to beat Shaina in order to move onward, Marin sits down on a rock to watch Seiya's battle against Shaina, reacting in shock as she notices Shaina using the "Thunder Claw". As Seiya finally splits Shaina's mask and ends the battle, Marin watches as Seiya makes way back to Japan.
Silver vs. Bronze
After the Flame Saint's defeat by Ikki, the Pope decides to send the Silver Saints in order to dispose of the Bronze Saints in order to reclaim the mask of the Gold Cloth.
Marin is sent along with Misty in order to kill Seiya, and they find him by the beach. As Marin notice Seiya trying to fight Misty, she grabs her student and punch straight through his heart, killing him.
However, as Marin walks away after they bury Seiya, she persuades herself to not look back, revealing that it was only an illusional attack. When Seiya finally defeats Misty, Marin thinks she will be unable to return to Sanctuary now.
She later arrives back at the beach along with Moses and Asterion. When they notice Misty dead and Seiya gone, Asterion and Moses ask Marin what happened. Refusing to answer, Marin attacks Moses with her "Ryu Sei Ken", but since Asterion is able to read her mind, she is easily grabbed from the air and defeated by Moses' "Kaitos Spouting Bomber", before they strap her out in the ocean to drown, unless Seiya manages to rescue her.
She is however rescued by Kiki, and arrives in time to save Seiya by killing Asterion herself.
The battle of the Twelve Houses
Marin makes an appearance again as she tries to reach Seiya after hearing from June that the Bronze Saints were going to challenge the Grand Pope and the Gold Saints.
She is however stopped in her tracks by Jaki, who easily beats her with his giant body. But as he is about to crush her, Marin leans backward, making both her and Jaki fall down the abyss, where Jaki is killed, but she manages to survive with great injuries.
A long time later, when she moves onward, she is stopped by Phaeton and several Sanctuary soldiers who give her a rough beating, until she is saved by Shaina's arrival, fighting fiercely back against the soldiers before running off with Phaeton while Shaina stays behind to deal with the rest of the soldiers.
Demon Rose Path
When she arrives at the rose path to the Pope, she finds Seiya unconcsious among the roses and gives him her mask in order to restore Seiya's concsiousness, before shortly falling for the roses herself.
Statue of Athena
After Seiya manages to defeat Saga, Marin arrives and tries to wake up Seiya who lost consciousness after the battle.
Marin arrives in Asgard in order to find Seiya and warn him about Syd's dark secret. However, before she can make it that far, she's spotted by Alberich and she is forced to fight the God Warrior. Although she manages to gain the upper hand slightly, she is defeated and trapped in a huge amethyst by Alberich.
After Shiryu finally manages to defeat the God Warrior, Marin reveals to Seiya that he should be careful, as she learned from Aldebaran that when Syd attacked, Aldebaran could feel another fist attacking him from behind, meaning that fighing Syd would mean fighting two opponents at once.
Antarctic Mammoth Pillar
Shortly after Shiryu succesfully destroys the Indian Mammoth Pillar, Seiya suddenly encounters Marin while looking for a new Pillar to destroy. He follows her until he reaches the Antarctic Mammoth Pillar, where he once again encounters Marin, who take off her mask and reveals herself as Seika, Seiya's sister. As they embrace, Marin suddenly stabs Seiya in the stomach, critically injuring him, revealing herself as an illusion created by Kasa.
While Seiya and his friends join the Gold Saints in invading the underworld to defeat Hades, Marin and Shaina remain at the Sanctuary along with Kiki and the Bronze Saints Jabu, Ban, Ichi, Nachi and Geki in order to defend it, should more Specters arrive.
While Seiya fights Thanatos, Marin brings back Seika who have searched for Seiya but lost her memory after a fall she suffered, forgetting all about her little brother. As Thanatos tries to kill her, the Saints defending Sanctuary combine their Cosmo in order to defend Seika, but they are all beaten down in the end.
When Hades is finally defeated, Marin and the others rejoice as they witness the "Greatest Eclipse" passing by the sun.
Being a Silver Saint, Marin is able to launch attacks at Mach 2, easily surpassing the Mach 1 speed of the Bronze Saints. When she burns her Cosmo, she is surrounded by a blue aura.
Ryu Sei Ken: Being Seiya's mentor, Marin can also use the Ryu Sei Ken, although at Mach 2 as she is a Silver Saint.
Eagle Toe Flash: Marin jumps into the air, then spreads out her arms like eagle wings, before landing a powerful kick to her enemy, resembling an eagle striking it's claws into it's prey.
Marin wears the Eagle Silver Cloth which covers little of her body, in spite of being a Silver Cloth. She has armor on her knees, the lower legs are covered by white clothing, only her left arm has protection on her lower arm and a little portion of her upper arm is protected. She has a shoulderplate on her left side only, leaving two black straps on her right, a collar protects her throat and she has a tiara which covers her head.
- Although Marin is a Silver Saint, her rank was not revealed until the arrival of Misty.
- Marin can use the same Ryu Sei Ken as Seiya, although she does not shout out "Pegasus" while striking.
- Marin's Silver Cloth covers less of her body than Seiya's Bronze Cloth, whereas a Silver Cloth should offer more protection than a Bronze Cloth.