As expected of Rudeus.-Eris, on several occasions
Eris Boreas Greyrat (エリス・ボレアス・グレイラット Erisu Boreasu Gureiratto) is a noble girl and distant relative of Rudeus. She is a tsundere character with a short temper but has potential in the Sword-God style. During her journey to return home following the teleportation incident, she grows to love Rudeus.
She has long red hair, a nice figure, and swords around her waist on both the left and right sides. At the end of the Decisive Battle Chapter, she has streaks of white in her hair due to mana strain.
Before meeting Rudeus, Eris is violent, strong, tomboyish, and merciless taking a personality and mannerisms similar to Sauros. During her time with Rudeus she still maintains her violent tendencies but she has greatly changed after her tenth birthday and will resort to violence to anyone who holds negative emotions and or intentions against Rudeus. However, despite the outer aggressiveness, Eris also has a high level of shyness, often hitting Rudeus for touching her suddenly even though she does the same to him. She and Rudeus have a mutual inferiority complex where both would assume the other is more wonderful than themselves, easily leading to misunderstandings which also causes her to leave Rudeus and went to train in the Holy Land of Swords to be on equal standing with Rudeus.
During her time on the Holy Land of Sword, Eris became taciturn and uncaring as she obsessively trains to become stronger while recalling the memories of her defeat from Orsted and the sight of Rudeus in a near dead state. She also does not interact nor talk with with almost anyone unless its a topic about Rudeus until she trains together with Nina and Isolte Cruel. 
Eris gets excited easily on seeing things she have never seen before like the Migurd Village houses that uses giant turtle shells as roof tops in the Demon Continent. When Eris enters the Chaos Breaker, she raises her voice in amazement upon seeing how small the village is from the sky causing Sylvaril to take an immediate liking to her upon seeing Eris' carefree smile and offers to guide her around the castle. 
Originally, she had a tendency to constantly release blood lust, but later controls it after years of training at the Holy Land of Swords. She is named the 'Mad Dog' or Mad Sword King due to her personality of bearing fangs at anyone for a period of time and is noted to be 'free'. She also has a high libido, often attacking Rudeus but it was later toned down after aging.
Her full name is Eris Boreas Greyrat. The Boreas was one of the great noble families in Asura Kingdom who rules the Fittoa Region. Her behavior prior to meeting Rudeus was uncontrollable and violent. She was considered a failure as a noble. After the Teleportation incident, she was accompanied by Rudeus and Ruijerd on her way to Central Continent. Sometime after starting her training in the Holy Land of Swords she relinquished her Boreas name. 
When Eris arrives at the Holy Land of Swords, Gal took interest in her potential in the sword to cut down Orsted, a dream he also shares despite Eris calling him a small fry that Gal laughs off in amusement. After defeating Jino Britts and Nina, Eris fights Gal and gets immediately knocked back by Gal's Battle Aura causing her body to fly outside, smashing down the gate in the process, and smacked into a pile of snow. Gal then tells Ghislaine to tend to Eris' wounds and bestows her with Saint Rank of the Sword God Style and personally foresee her training. 
For the next 6 months, Eris trains and swings her sword on a peninsula located north of the dojo that she found after an hour of walking to avoid interference from other students. One day after returning from her sword practice, Auber Corvette is standing in her way to the dojo and she tells him to move before Auber can finish his sentence eventually causing Eris to release a huge amount of bloodlust and a fight ensues. Despite losing her sword during their fight, Eris continues to attack causing Auber to get a chill on his spine and realizes he needs to kill this beast to stop her but Gal stops the fight. Eris collapse on the snow breathing heavily and frustrated then Auber mentions to Gal that it is his first time meeting such a serious swordsman and realizes she is the Mad Dog that Gal mentioned. Eris stands up swaying like a ghost causing Auber to ready his sword upon seeing this but Eris just glares at him and returns to her room to rest. One year later, Eris becomes a North Saint with Auber's training. 
This is the current achievement that Eris gained through her adventure, action, and training:
- Sword King
- North Saint
- Elementary Fire Magic
- Defeated Gal Farion with Ruijerd's help
- Defeated North Emperor Auber Corvette with Rudeus and Ghyslaine
- Defeated North King Twin Swords Knuckle Guard
- A ranked Adventurer
- Chopped off Dragon God Orsted's arm
Orsted: "Eris Boreas Greyrat, huh? Is he that important to you? Someone who isn't Luke."
Orsted: "The man fated to become your husband."
Eris: "I don't know anything about that."
Orsted: "It seems so." 
Eris: "I'm fine with waiting. I'll attack together with Rudeus."
Orsted: "... That's surprising. Eris Boreas Greyrat will fight together with her companions. Is this also a part of your madness? Certainly, if Eris Boreas Greyrat held a little more judgement, if she were to study under a suitable master, I see... So this is what happens?"
Eris: "I'm no longer a part of Boreas. It's just Eris Greyrat."
Orsted: "The Eris I know, is a different person, is she..." 
- Eris is the goddess of War in the religion Rudeus has created. A wooden sword is currently taking the place as her symbol and is enshrined in the basement.
- Eris name possibly comes from Greek mythology that is the Greek goddess of chaos, strife, and discord. Her name is the equivalent of Latin Discordia, which means "discord". Eris' Greek opposite is Harmonia, whose Latin counterpart is Concordia. Homer equated her with the war-goddess Enyo, whose Roman counterpart is Bellona. The dwarf planet Eris is named after the goddess, as is the religion Discordianism. Other names also come from Greek mythology like Anemoi, Boreas, Zephyrus.
- When Eris left Rudeus after their first time together, she left her panties and stole a pair of Rudeus' underwear. While in his depression-like state, Rudeus threw Eris' panties into a heating stove.
- In some previous loops where Rudeus didn't exist, Luke courts Eris and eventually the pair get married. In that timeline, Eris only has the potential of Sword Saint.
- In Orsted's previous loops, Eris is known as Red Lion instead of Mad Dog/Mad Sword King who also the second person needed for Ariel Anemoi Asura to become queen and along with Luke as her bodyguard would fight off numerous assassination attempts on Ariel and paving the way for Ariel's ascent to Asura Kingdom's queen
- Like Paul Greyrat, Eris is the second character in the story to relinquish her name and nobility status.
- Rudeus once referred to her as his Husband when he thought Zanoba might be confessing to him because in their relationship, Eris is the more sexually aggressive one and she made him feel like a maiden in love. While he gives arm pillows to his other wives, he would get one from Eris.
- Eris became the husband after she defeated Rudeus in bed on their first wedding night. Rudeus dominated the battle until his physique allowed it but Eris' stamina overcame him and he accepted his defeat happily at the end.
- Eris considers that she is only good at 2 things: with the sword and at sex.
- While Rudeus has a Harem consisting of his wives, Rudeus considers himself a part of Eris' Harem, which consists of himself along with Rinia and Pursena.
- Even though Eris is quite wild in bed she is very shy about showing this to other people. Rudeus suffered a lot to convince her to do a 4 P.
- Like all who have descended from the Boreas Greyrat Household, Eris has inherited a love for Beast Girls. In addition, she also is fond of dogs and cats, possibly an extension to the inherited trait.
- Despite being very jealous even with Rudeus's other wives, she has no problem with Rudeus sleeping with a slave(Rinia), due to the teachings of her family although Rudeus refused Eris' offer to sleep with Rinia since he considers it a betrayal of his wives.
- Even though she learned language, math, science, and etiquette in her childhood, she forgot all of them later on and can only read easier words.
- Out of all of Rudeus's wives, Eris is the only one with large breasts. Because his other wives all had very small breasts, she and many others mistakenly assumed he only liked small breasts.
- Eris dies at the age of 74. Despite her age, she was still training very energetically, one day after her morning run and after practicing with her sword, she returned home tired and collapsed in bed, then passed away from old age.
|Family Head||Rudeus Greyrat|
|Members||Paul Greyrat • Zenith Greyrat • Lilia Greyrat • Norn Greyrat • Aisha Greyrat |
Sylphiette • Roxy Migurdia • Eris Boreas Greyrat
Lucy Greyrat • Lara Greyrat • Ars Greyrat• Sieghart Saladin Greyrat
|Servants||Rinia Dedorudia • Pursena Adorudia|
|Pets||Leo • Beat • Jirou • Matsukaze|
|Members||Eris Greyrat |
|Temporary Members||Vizquel • Geese • Jalil|