Eterna Rinebow

Appearance
Despite being at least sixty years old, she has the appearance of a teenage girl. She has the appearance of a typical witch. She has a large, oversized hat along with blue beads attached to it. She has bright pink eyes and long blue hair.

Eterna has two round bird creatures that accompany her that help her with her magic. As shown in the manga, they appear to reflect her opinion on other characters.

Personality
Eterna generally comes off as a stoic person, and isn't afraid to speak her mind. While Flum admits she sometimes doesn’t always get how Eterna feels about something, Eterna also shows a rather caring side, and she is loyal to those she cares about. This was shown when she willingly decided to help cure Milkit’s poisoning without much prompting. During Episode 04, while she was tempted to leave Flum, Milkit, and Ink behind, she decided her life with them was far more important to her.

If something angers her, she will not hesitate to show it as she could not hide her shock and disgust when she finds out that Jean sold Flum into slavery. She becomes even angrier when she finds out Jean told Flum that she and Gadhio along with the other members of the Hero Party were in favor of selling her.

After becoming Flum and Milkit’s roommate, she demonstrates a playful, teasing side, and she is open to the idea of homosexuality. She loves teasing both Flum and a Milkit regarding the status of their relationship. She is strongly in favor of the two of them getting together. The narration indicates she is glad that Flum and Milkit make each other happy.

Eterna also can be protective of others, but she is respectful of other people’s wishes as well. During Episode 03, she offers to help Flum deal with Dein, but she respects Flum’s request to protect Milkit while she is out in the city. When Dein’s men do attempt to kill Milkit, Eterna casual wipes them out due to her disgust at how they would attempt to harm someone as helpless as Milkit.

While Eterna outright states she isn’t a teacher, she is willing to teach those that are interested and willing to learn. During the their time in the Hero’s Party, she taught Flum quite a bit about herbs to the point Flum knew Milkit was inflicted by Mustardo poisoning, and she knew what herbs were necessary to make a cure. During Episode 03, she teaches Flum a few things regarding magic that prove to be invaluable to Flum learning how to use her Reversal Affinity offensively in battle outside of equipping Cursed Equipment.

History
When Eterna was a child, she was chosen to be a test subject by the Church of Origin. During her time of being experimented on, she was adopted by the Rinebow family who taught her many things, such as about medical herbs.

Eventually, some time after earning the title of the Timeless Witch, she is chosen by

Episode 01
Eterna is introduced, along with Gadhio, going on a shopping errand with Flum. She along with Gadhio offer to help Flum with her shopping.

When Jean sells Flum into slavery, Flum has a hard time believing that Eterna and Gadhio would sell her. Jean merely tells her they agreed because Flum is more of a burden on them than any of the others. However, it was a complete lie.

After Jean lies to the Hero Party that Flum left on her own accord, Eterna seemed disappointed that happened.

Episode 02
During the battle with one of the Demon Generals, Eterna becomes irritated by Jean’s attitude and blaming her for the battle not going well. That along with Flum’s departure cause her to decide to leave the Hero’s Party. After discussing it with Gadhio, Eterna says farewell to the other members before making her exit.

Toward the end of the Episode, Eterna is found by Flum and Milkit squatting in Flum's House. Flum was rather surprised to find Eterna there while Eterna was surprised that Flum was still in the Capital. She then noticed Flum had a Slave Crest on her left cheek, and she inquired about how she got that. It was then she learned that Jean had lied to them about Flum leaving to go home, but he had actually sold her into slavery. Likewise, much to her anger, Jean lied to Flum by telling her that everyone, including Eterna, approved of selling Flum into slavery.

Understandably, Eterna was angered by this revelation, but she also showed sympathy regarding what happened to Flum. She also was sympathetic when she noticed Milkit suffered from Mustardo poisoning. When Flum provides her with the necessary herbs to cure Milkit, Eterna immediately agrees to make it.

While Eterna was willing to leave the house if Flum didn’t want her, Flum happily accepted Eterna as a member of the household. For the following few days, Eterna works on Milkit’s treatment and succeeds in curing Milkit.

During the side story, Eterna pokes fun at how Flum is aroused at the idea of seeing Milkit’s face.

Episode 03
Eterna is an established member of Flum’s household. After becoming a member of Flum’s house, she continues her experiments. She also attempts to creat her own tea to sell, so she can avoid being a freeloader to Flum and Milkit. Also much to her chagrin, her desk ends up being housing a number of handcrafted figures of Flum that Milkit made.

Eterna develops a connection to Ink Wreathcraft, who Flum takes in, due to their shared history of being experimented on the Church.

During the first half of the Episode, Eterna offers to help Flum deal with Dein Phineas, who had been causing Flum and Milkit a lot of trouble ever since Flum became an Adventurer, but Flum refuses. Instead, she asks Eterna to keep guard of Milkit. This proves to be wise as while Dein attempts to kill Flum with his men and corrupt guards, Dein sent a number of men to attack Flum’s house and kill Milkit. Eterna makes short work of them.

Eterna manages to save Ink’s life by removing the Origin Core in her body and transplanting Dein’s heart.

Episode 04
During Episode 04, it was revealed that Flum's House, used to belong to Eterna’s adoptive parents.

Eterna is offered a chance to have a new life with her resurrected parents, but she decides the new life she has formed with Flum, Milkit, and Ink is more important.

Episode 05
At the end of the Episode when Flum is in Cyrill’s arms, Eterna teases Flum about ‘cheating’ on Milkit much to Flum’s chargin.

Abilities/Equipment
Water: Eterna has the ability to use water. She is able to use it for both offensive and defensive purposes.

Extended Lifespan: Due to tue experiments Eterna was subjected to, her lifespan was greatly increased as the aging process was reduced. Despite being at least sixty years old, she still has the appearance of a teenager.

Medical Knowledge: Eterna is highly intelligent, but she is extremely proficient in knowledge regarding medical herbs. She also knew enough to be able to conduct surgery.

Roommates
As a whole, Eterna is shown to care for Flum, Milkit, and Ink. During Episode 04, she was given a tempting offer to have a new life with her reassurrected parents, but she knew that would mean betraying them. In the end, she choose to be loyal to them because she believed the new life she formed with them was more important. She is also shown to be protective of her roommates, especially Ink.

Flum Apricot

During their time in the Hero’s Party, she along with Gadhio were the only ones to consistently treat Flum well. Likewise, Flum was one of the only people she considered to be a friend. She taught Flum about herbs, helped her with errands, and she liked having Flum around. After Flum ‘left’ the Party, she quickly lost interest in remaining part of the group, especially due to Jean becoming even more difficult to deal with, so she left the group.

Towards the end of Episode 02, Flum and Eterna are reunited. Eterna learned the truth regarding Flum’s departure, and she made it clear she had no knowledge of Jean selling Flum into slavery. She was especially angry that Jean lied and told Flum that she approved of such an action. She was willing to get revenge for Flum if she knew where Jean was or had access to him.

When Eterna was willing to move out of Flum’s house, Flum was more than willing to let Eterna stay as a roommate. Eterna was also more than willing to fulfill Flum’s request to cure Milkit’s face after being provided with the necessary medical herbs.

During Episode 03, Eterna was willing to help Flum deal with Dein Phineas, but she respected Flum’s wishes to protect Milkit. She did show concern for Flum’s wellbeing, but she honored Flum's wishes and kept her promise. Likewise, Flum was concerned for Eterna when Eterna was forced to flee from the mysterious 'Eyes' that attempted to kill her, and she was glad to see Eterna was alive and well.

Milkit

Shortly after meeting her, Eterna was quick to diagnose that MIlkit was infected by Mustardo poisoning. She also displays disgust on how cruel someone must’ve been to do something like that to Milkit. Upon receiving the necessary herbs from Flum, she quickly agrees to cure Milkit’s condition to which Milkit was grateful to both Flum and Eterna for.

The two are consistently on good terms. Eterna treats Milkit well, and she doesn’t look down on Milkit due to her past as a slave. Likewise, Milkit is respectful of Eterna, and makes sure to do a good job cooking her meals as well.

When Flum is not around, Eterna acts as Milkit’s protector, as per Flum’s request. This was best demonstrated in Episode 03 when Eterna defended Milkit from Dein’s men who came to burn down the house and kill Milkit. Due to how the men were attempting to murder Milkit and potentially do worse to her if she survived, Eterna didn’t care what happened to them when she literally used her power to wash them away. Milkit was briefly surprised by this display of power, but she agreed with Eterna’s mindset.

Ink Wreathcraft

Due to the two having similar backstories with being experiments of the church, Eterna saw Ink as a kindred spirits to an extent.

Eterna played a major role in saving Ink’s life from the Origin core.

During Episode 04, Ink showed some insecurities about being blind and not useful. Eterna makes it clear that she enjoys Ink's company. After Satils turned Eterna's parents into monsters, she didn't hesitate to kill them and protect Ink.

Other Allies
Gadhio Lathcutt

He was the only other member of the Hero’s Party that Eterna got along with besides Flum. When she decided to leave the Hero’s Party, she told Gadhio about it first, and he was fine with it. In Episode 03, Eterna correctly guesses Gadhio would leave the party soon as well.

Welcy Mancathy
Eterna repected Welcy's ability to gain information.

Enemies
Jean Inteige

Even before find out he sold Flum, Eterna and Jean got along as well as water and oil. She left the party partly due to his poor attitude. When she finds out that Jean sold Flum along with lying to her that she and Gadhio were infavor of selling Flum, she becomes rather angry. When asked about Jean by Milkit, she makes it clear that she would give Jean a piece of her mind if she ever were to cross paths with him again.

Dein Phineas

While Eterna only interacts with Dein once, is very much aware of what kind of person he is from what Flum told her. During the first half of Episode 03, Eterna was willing to help Flum take him out, but she told her to remain at the house to keep Milkit safe from him. This proves to wise as Dein sent men to kill Milkit that Eterna easily dispatched.

Trivia

 * In the manga, the bird creatures Eterna has seem to mirror the opinion Eterna has of other people. They showcase her distaste for Jean.  By comparison when they saw Flum, they were rather happy as indicated by the ‘heart symbol’ over its head.