Derieri/Plot

Albion arc
After Hendrickson managed to remove the seal, Derieri and the rest of the Ten Commandments appeared before the terrified former Great Holy Knight and Fraudrin in Dreyfus' body with Zeldris uttered Meliodas' name as if he knew him. After being informed by Fraudrin of the current events in Britannia, Derieri asked why there were so few of the other 4 races as well as claiming to be tired and wanting rest. Zeldris suggested that they should head for Edinburgh Hill for recuperation of their severely drained magical powers due to the seal they're trapped in, which everyone agreed and left Zhuhur Valley by flight, leaving a terrified Hendrickson.

Arriving at Edinburgh Castle, Derieri and her fellow Ten Commandments find a castle in ruins and a giant hole, Derieri asks what happened because she is confused, they conclude that it was Meliodas who caused it. After Galand left to take a look at one of the destroyed Albions, she and the others then discuss how to recover their power faster, and begin to collect souls to eat, as a way to both recover their magic faster as well as exterminate the humans. Derieri sees two humans and eats their souls stating it was "Two Birds, One Stone", meaning humans souls are good for replenishing their magical power faster.

When Galand returns and explains he killed Meliodas, Derieri is asleep in Monspeet's lap.

Istar arc
Later, Meliodas unexpectedly pays the Ten Commandments a visit, during Meliodas’s battle with Garland, Monspeet protects Derieri from the collision. After easily defeats Galand, and warning the Ten Commandments if they get out of line, he and the Seven Deadly Sins will crush them. In response Zeldris orders them all to head off to more quickly regain their magic and exterminate the other races. She and Monspeet then head to a town known as Bellford.

Great Fight Festival arc
She and Monspeet continue their purge in the north of Britannia, having devoured the souls of almost every person in nine cities and villages and showing no signs of stopping.

Later on she, along with the other Commandments, arrive to aid Drole and Gloxinia, who are facing off against Meliodas. After Grayroad has ensured that Meliodas cannot escape, Derieri immediately goes on the offensive exchanging blow after blow with Meliodas. Due to her power, Combo Star, she quickly gains the upper hand and seemingly causes his demonic powers to fade, renders both his arms useless, and then throws him into Monspeet's arms. She watches as Meliodas almost cuts Monspeet's head off, and makes a remark he does not even want to understand. After Meliodas is defeated, she tells Estarossa that she feels someone watching them, and wonders if they really should just let them be. Then, after Estarossa kills Meliodas, Derieri along with the rest of the Ten Commandments leave.

Defensive Battle for Liones arc
As the Ten Commandments move to take Castle Liones, Derieri and Monspeet watch as Estarossa battles Escanor. She says Escanor is a monster and is surprised he has the upper hand in the battle. After Estarossa is defeated, Monspeet suggests they should go help, but Derieri says they rather have to overthrow the castle.

As she and Monspeet arrive at Liones Castle, Denzel arrives, announcing to protect the kingdom by killing the demons, and allows the goddess Nerobasta to use his body as a vessel in order to fight the Commandments. Enraged at the sight of a goddess, Derieri says she will kill her alone. Shortly after entering Denzel's body, Nerobasta states her name and rank, and asks what mission she has been tasked with. Upon seeing demons, and specifically Derieri she becomes enraged that the seal on the Demon Clan has been broken. When Deathpierce explains the situation, she refuses to help and attempts to flee, killing a red and gray demon on her exit with her attack Ark. The onlooking Monspeet muses that the usage of light magic is typical of the Goddess Clan and the opposite of the Demon Clan's own darkness.

Derieri takes to the skies and Nerobasta, following her, attempts to kill Derieri with Ark, but she negates the attack with her darkness, merely having most of her hair disintegrated. Nerobasta then attempts to behead Derieri, but she uses her darkness to cover her neck, breaking the blade. Nerobasta, realizing she's outmatched, attempts diplomacy, stating she understands why Derieri might hate her and her people for breaking the treaty and killing demon children, but before she can finish, Derieri bifurcates Denzel's body, killing her.

During the battle to take Liones, Derieri and Monspeet notice a strange disturbance and go to see what it is. When they arrive, they find a giant pig causing havoc, being ridden by some unusual travelers. Originally curious at Elizabeth Liones's resemblance to a person she once knew, Derieri later became enraged when Elizabeth uses Ark on her and attempts to kill her only to be blindsided and seriously wounded by Meliodas. She falls off the pig and Monspeet rushes to her side. Once Derieri regains consciousness, she spends a significant amount of effort to heal her wound with her darkness. Getting over the initial shock of seeing Meliodas alive, she devises a plan to kill him again. She tells Monspeet that she will distract Meliodas, and when the opportunity presents itself, he should hit both of them with his strongest attack. Monspeet at first feigns ignorance of what she means, but she assures him that she will survive the attack as she believes that she is much tougher than Meliodas.

She then charges off and Monspeet summons many lesser demons to help Derieri build up her Combo Star ability. After hitting 51 demons, Hawk Mama and Hawk, Meliodas blindsides her again by pile driving her into the ground thus resetting her combo. Enraged, she begins attacking Meliodas again, screaming at the traitor, but he easily parries all of her blows until attack number 12, in which he resets her combo once again by dodging her punch and hitting her from behind.

Meanwhile, Monspeet positions himself in the sky right above the fight. As Derieri tries to build up new combos, which are continuously parried by Meliodas, the latter admits that he would rather not kill his former comrades. As Monspeet then unleashes his Kaijinryu, Meliodas specifies that his previous statement is something the old him would have said and proceeds to kick Derieri into the sky. He then activates his Black Mark and uses Full Counter with a sinister smile on his face, telling them to die. Monspeet rushes into the fray to save her, but they are both apparently consumed by the rebound.

Prelude to the New Holy War arc
When Zeldris calls telepathically to the other members of the Ten Commandments, Derieri and Monspeet reveal themselves to be alive. However, both decide not to respond to Zeldris, as they have decided to stand by the side of the battle and stay in a peaceful life in the hut of humans who had given them asylum after they got rid of a bear that caused disasters on their farmland. Derieri ask Monspeet if he really is fine with that kind of life and calls him weird when says that is fine because there is nothing that makes him worries over her. There, they both discuss the reason Meliodas forgave their lives, as Elizabeth had done 3,000 years ago. When the farmland girl comes with some food and drinks, Derieri runs to her and quickly eats a loaf of bread, while the girl tells her that the clothes she borrowed fit her very well.

New Holy War arc
Sometime later, after the new Holy War began, Derieri is still with Monspeet residing in the human village. While relaxing there, they notice that war broke out, but instead of participating they are hiding out with the humans. Derieri however says she does not care and asks what he wants to do. Monspeet tells Derieri he would rather live peacefully with her, but if Zeldris finds them they will be punished, and the village as well. Derieri gets up and tells Monspeet that she is going to surrender her commandment to Zeldris, as the mark in her cheek fades away. She tries to explain why she would surrender her commandment but can not put it into words and Monspeet comments on it is been a long time since he is seen her talk. Derieri comments on how her sister would have wanted her to talk to Monspeet and how her sister loved him.

They are then interrupted by the farmland girl who is killed in front of them by Estarossa. Furious, she charges at Estarossa, but he uses Full Counter which causes her to be knocked back and caught by Monspeet. Estarossa attempts to eat the farmland girl's soul but Monspeet saves it using Trick Star and gives it to Derieri telling her to escape with the soul. Instead, Derieri releases it and attempts to join Monspeet in fighting Estarossa. She is stopped by Monspeet warning her to retreat, this causes Monspeet to get distracted and gets put in a head lock. Derieri yells at Estarossa to stop it and that she was already planning on surrendering her commandment. Monspeet says that he was too so that he could tell her the words he is kept hidden in his heart, causing Derieri to blush. As Monspeet's neck is rendered immobilized he uses Conjurer Joke to switch places with Estarossa, and he begins explaining why Estarossa could not take in their commandments because he would die. Estarossa eventually passes out and Derieri starts walking towards them thinking they had won and asked what they should do with him. Monspeet warns her but it is too late and Estarossa awakens and grabs her throat, preparing to stab Derieri. Monspeet uses his last Conjurer Joke to switch places with Derieri and has his last heart impaled instead.

After Estarossa crushes Monspeet's last heart, Derieri watches in shock and sadness. Monspeet then sent Derieri far away from them, so she can escape Estarossa, as she flies away she asks Monspeet what it was he wanted to tell her for so long. Monspeet tells her he can not tell her since he cannot be by her side anymore and engulfs both him and Estarossa in a Hellblaze. Derieri then screams out his name as she watches him fight to the death.

Derieri then arrives in the middle of the battlefield of the Search-and-Destroy Force. The forces all express shock that one of the Ten Commandments is there. Deathpierce uses this opportunity to get revenge for Denzel and attempts to cut off her head, but his sword simply break on Derieri's skin due to her body's resilience, and she walks past him without any intent on fighting. Elizabeth arrives and asks her what is wrong and why she is there to where a heartbroken and destroyed Derieri explains about Monspeet's sacrifice and death at the hands of Estarossa. Estarossa himself then appears dashing towards Derieri. Elizabeth proceeds to protect Derieri and puts herself in front of her. Then, Estarossa surrounds the alliance army and Derieri as well, telling her that he will have her commandment, and she will see Monspeet soon. Derieri then watches in amazement as Elizabeth uses "Ark" on Estarossa.

While Estarossa is battling Sariel and Tarmiel, Derieri and Elizabeth are still trapped by Estarossa's Evil Hound technique. After Elizabeth eliminates the black flames, Derieri mutters to herself confirming that that was the goddess Elizabeth's power. As Elizabeth shouts out for her teammates, Derieri remain calm and tells her they are most likely dead because of the effects of the hell fire. Diane and the rest of the allied forces reveal themselves to be alive, surprising Derieri.

While Sariel and Tarmiel fights Estarossa, Derieri talks to Elizabeth about Monspeet's death. She asks her if she knew what Monspeet wanted to tell her all this time and how he was always by her side protecting her. Elizabeth tells her she does not know but that she and Monspeet are similar to her and Meliodas; she explains that she wants to do whatever she can to compensate for Meliodas' suffering and sacrifice; that maybe Derieri did not know about what Monspeet wanted to say, but the important thing is how she feels.

The archangels return announcing the demise of Estarossa, but immediately Estarossa appears alive, under a transformation. She watches as he battles against the two archangels. Then she tries to prevent them, as she realizes that Estarossa absorbed Galand's decree. Derieri notices that he also is in possession of Monspeet's decree. Derieri and the forces look on in shock and fear as Estarossa changes aspect once again, presenting himself as the "great Meliodas".

Derieri and the rest of the alliance watch Estarossa in shock as he has become a new being after absorbing two commandments. Estarossa tells Elizabeth that he wanted to see her for so long but midway he focuses his attention on Derieri. Estarossa says to Derieri that he has come for her commandment. She tells Elizabeth that he has become mentally unstable, explaining that if anyone other than Zeldris or Meliodas absorb more commandments other than their own they would be destroyed.

Estarossa keeps approaching both Derieri and Elizabeth switching motives and individuals as he walks towards them. Derieri then watch in shock as holy knights, Sins, and Archangels tries to futilely stop Estarossa.

Before Estarossa could annihilate her friends and comrades, Elizabeth shouts to him to stop, that she will follow him willingly. She then asks the rest of the alliance to protect Derieri. Derieri watches as Estarossa takes Elizabeth away.

After that, Howzer decides to keep going south to Camelot, while sending a team composed by Sariel, Tarmiel and King with the task of defeating Estarossa and rescue Elizabeth. Derieri decides that she wants to go along as well and help. Sariel and Deathpierce berate her saying that she has no purpose in going and lacks the trust of anyone within the force. King says that he trusts her, as he trusts Elizabeth who saved them a long time ago. Derieri confused and shocked asks King how he knew about that. Then the group departs in their mission.

On the way, King thanks Derieri for helping them rescue Elizabeth. Derieri affirms that this is not her only objective, since she also wishes to obtain his revenge against Estarossa. However, Derieri begins to feel surprised when pronouncing his name.

Upon arriving at the Celestial Theater and finding Estarossa engulfed in a mass of darkness with Elizabeth locked up inside of it, the four confront him. While defending herself against his attacks, Derieri asks Estarossa to tell who he really is, affirming that there is no one with that name in the Ten Commandments.

Then Derieri, along with all those who once knew "Estarossa", is freed from the spell that altered their memories, revealing the true identity of Estarossa as Mael of the Four Archangels.

While Mael recovers his memories and battles King, Gowther, Sariel and Tarmiel, Derieri goes to the aid of Elizabeth who had been liberated from his darkness. Upon awakening, Elizabeth cries that she does not know what to do to save Mael's heart from the commandments. Elizabeth apologizes to Derieri for speaking in front of her to save whoever snatched her most precious person, however, Derieri says they must save Mael, just as Elizabeth saved her and Monspeet.

Derieri starts talking about how they both died the moment they become Induras 3,000 years ago, when they were saved by Elizabeth and Meliodas. She says that in the past they blindly followed orders to kill the other clans without ever questioning them, just believing it was what they should do, not even stopping after having been saved by their enemies. Derieri expresses that she believed Meliodas a fool for betraying them, but that now he realizes that she is the fool and that she does not know why take so long to see it. Derieri says that Monspeet was always at her side like her other half, and that what she most wanted was to have him with her. She declares that she cannot ignore what is happening and that she must stop the Holy War and stopping Mael is the first step. Elizabeth asks how they could do it, when she was unable to take away the commandments. Derieri says she has a plan and leaves to the battle, telling Elizabeth to stay behind.

Derieri improvises a plan on how to challenge Mael and possibly defeat him, asking Gowther to relay the message to everyone but Mael himself: Sariel and Tarmiel would restrain Mael with their powers and while restrained, Derieri would use her Combo Star to render Mael incapable of countering, Gowther would use that opening to scan the Archangel's memories, searching for the spell that remove the Commandments.

Everything goes according to plan, but, as Mael is being struck from all corners, he appeals to Tarmiel and uses the guilt that they are attacking his own brethren. Tarmiel falters and stops using his ability to restrict Mael's movement. In that instant, Mael shoots a blast of Kyusai no Ya piercing Derieri's chest, destroying her last heart in the process.

Derieri, fatally wounded, falls to the ground as Mael begins to remove her Commandment. Elizabeth shouts her name and catches her.

Derieri then wakes up in a strange but familiar place, where she realizes she was killed by Mael. She then hears Monspeet's voice and turns around to see him talking about Meliodas betraying them. Derieri talks back to him, but then, surprised, Derieri sees that Monspeet was talking to another Derieri, realizing then that she is having a vivid reminiscence in the Demon Realm, 3,000 years ago. She hears again Monspeet asking her if she is willing to follow Meliodas' lead, implying the two of them run away together. Her old self gets mad, believing he must be joking, and flies off to find Meliodas, followed by Monspeet. Derieri discovers Monspeet's previously unheard words, saying he was not joking, making her realize that Monspeet always told her how he felt but she was oblivious to that fact.

She then happily thanks both Monspeet and Elizabeth.

In the real world, Elizabeth, who was using the Druid Memory Spell on Derieri, cries over her dead body and places her in a grassy area to rest peacefully.

Her body is later seen after Mael's Jiai no Kougyoku ability causes Diane to redirect the magic attack using her Lightning Rod ability, causing the ruins of Heaven's Theater to break apart, sending Derieri's body dropping from the sky, but her body is safely caught by King using Chastiefol's eighth form, Pollen Garden.

In the aftermath of the battle, Mael uses a technique on both the bodies of Derieri and Oslo that allows the soul to move forward to a new life while keeping their memories of their past life. Mael states that he did this because in case they were to be reincarnated and wanted to punish him, he would accept it.