Family[]
Puck & Beatrice[]
Echidna created Beatrice and Puck 400 years ago. Beatrice refers to her as Mother, while Puck does not seem to be so fond of her. Despite that, they both show some degree of respect towards her, Beatrice even considers Echidna to be her actual mother.
Eridna[]
Like with Puck and Beatrice, Echidna made this artificial spirit with unknown purposes. That said, according to Eridna, she felt as though that her simple birth was the purpose on its own. Whether this is truly the case is unknown. Thanks to Subaru’s reaction to her declaring herself by the name Echidna, she came to realize that her creator did not seem to be a good person, and she wondered what she did to rile up such hostility in Subaru.
Ryuzu Clones[]
Echidna made numerous clones of Ryuzu during her research into immortality. Whether she made any headway is unknown, but she ultimately left them to guard the Sanctuary for her, creating a contract not to undertake the trials, and she even made it so that her apostles could command them. In particular, she would end up using the Shima clone when she broke this contract to save Garfiel, and she would end up taking over her body to become Omega.
Witches[]
Minerva[]
Among all the witches, Minerva is on the best terms with Echidna because she likes to take care of people like Echidna. Despite that, she did interfere with Echidna's forming of a pact with Subaru due to her own beliefs and the fact that she wasn't being entirely honest with him.
Carmilla[]
Carmilla does not seem to like the way Echidna does things, and Echidna will even lie to her to get what she wants, such as when she attempted to prevent Subaru’s mental breakdown by taking the face of Rem. When she panicked and vanished, she mentioned that this was not what she was told would happen, and when she appeared later to make Subaru feel the genuine emotions of Satella, she would even say that she didn’t like how Echidna was handling this situation.
Satella[]
As the Witch of Envy, Satella supposedly was involved with Echidna and the other witches' deaths. Unlike the other witches who only despise the Witch of Envy, Echidna hates Satella as well for a currently unspecified reason. The author has stated that Echidna opened her heart to the Witches of Sin, excluding Satella.
This said, according to Alec Hoshin, she and Satella traveled together alongside four others in a journey to save the world, before she ever became the Witch of Envy. How their relationship was in the beginning is unknown.
Hector[]
Hector and Echidna were in some sort of conflict when both were alive. Hector pursued Echidna which caused her to protect herself in the Sanctuary for a time. After seeing Roswaal badly wounded, she decided to fight him, the outcome of the battle remains unknown, though it is certain that Echidna survived, as it is known that she was later sealed by Volcanica.
Pandora[]
Unlike the rest of the world, Echidna seems to at least be acquainted with Pandora, describing her as the Witch of Vainglory to Emilia during her trial. However, she is dismissive of Pandora's power, claiming that it made her an expert at saving her own skin.
Sphinx[]
Sphinx was Echidna’s first “failure” in her research, having failed to pass on her emotions into her despite passing on a piece of her soul, and she would proceed to discard Sphinx. That said, Sphinx seems to be fixated on the goal she was given by Echidna, and she has spent 400 years attempting to complete it, involving herself in the Demi-Human War and masterminding the Great Disaster in her efforts. She even looked into the ever shrinking knowledge of the witch, coming to find multiple points of view of her between history and her own memory. Now, Sphinx calls herself the Witch of Greed after taking on Echidna’s appearance, though any further similarities are unknown.
Emilia Camp[]
Roswaal A. Mathers[]
Years before the Great Calamity, Echidna encountered a young Roswaal who was unable to utilize his insane magical talent and potential. He was being treated as a sickly nuisance by everyone who encountered him as back then, magic was very much misunderstood and the mages weren't as renowned as they are now (with few exceptions). Echidna sensed his ability and potentially devastating power and decided to take him under her mentorship, teaching him how to properly use magic, opening Roswaal's eyes and allowing him to recognize that his body isn't a "danger" but a "gift", allowing him to prevail and learn how to effectively use all six magical elements. As a result, Roswaal harbored intense and deep feelings for her, which were sadly for him very one-sided. Despite that, she still became the most important person to him, as even after her death, Roswaal became obsessed with reviving her; even being prepared to give his life in order to achieve his desired future and cross paths with Echidna once more.
Emilia[]
Echidna claims to have hated Emilia from the moment she first saw her. During her trial where Emilia was forced to face her past, Echidna made several derogatory remarks at the half-elf, mocking her for her dependence on Subaru. Echidna also seems to have some knowledge about Emilia's parents, claiming that she is just as stubborn as her mother. Echidna adds that she personally knows her real mother and that it is one of the reasons for her hatred. Another of the reasons why she hates Emilia is the fact that the half-elf is nice to her, even though Echidna constantly insults her.
For an unknown reason during one of the trials Echidna burst into genuine tears stating "You disgust me... I- just hate you so much" before disappearing.
It is stated that Echidna created Puck to watch over Emilia, thus making Echidna's connection to Emilia even more mysterious.
Natsuki Subaru[]
Subaru first met Echidna when he was invited to her Tea Party in Arc 4, where she muttered that he was early. In their talk, she would reveal herself as the Witch of Greed and even inquire as to any knowledge he might want, going into a small spiel about the other witches. However, Subaru decided against asking her anything, leaving Echidna shocked and attempting to get him to ask something of her. Disappointed, she would end up making him an Apostle of Greed, and she would make it to where he didn’t remember her until their next meeting. Shortly after, she would give him the chance to take the first trial and talk to illusory versions of his parents. Even though he knew they were simply illusions, he was still grateful to the witch for allowing him to talk to them again.
After his failed third loop of the arc, suffering from the mind-shattering pain of being eaten alive by the Great Rabbit, Echidna would invite him back to her Tea Party, saving his mind with the calming effect of the Witch’s Graveyard. Here, he would reveal to her his authority, which he could finally speak of for the first time to anyone. Echidna, however, seemed to have already been aware, and she would allow Subaru to relieve himself of the stresses that came with having to suffer. She even decided to let him talk to other witches, though she was reluctant about it. Shortly after, Echidna would make it so that he would remember her when he left the place, and she would even assist him by giving him a way to kill himself when he ended up being taken in by the shadows of the possessed Emilia.
The next time they would meet, however, would not be on good terms. Having sent Carmilla, the Witch of Lust, to save Subaru from the effects of the second trial by using Rem’s face and words, he would be angered by these antics. Soon after, she would strike him with a deal in which she gave him his guidance using Return by Death. On the verge of accepting, the other witches came in to stop her, and they would reveal to him her true intentions. Echidna was very intrigued by his authority, and she believed that it would allow her to experience numerous different experiences in various different ways. The negative side to a contract with her would be abusing the authority, and she had no issue with using Subaru similarly to a lab rat. It should also be stated that during their talks, he learned of the witch’s history with Beatrice. Hearing of the neglectful and cruel way she left her to guard the Forbidden Library simply to sate her own curiosity, his hatred of the witch grew. Because of all of this, Subaru came to realize her true nature and rejected her deal. Echidna did not seem to mind whichever choice he made, and it was even implied that she wanted him to say no. That said, she ended up revoking his appointment as an Apostle of Greed, making it so he could not freely enter her tomb.
Because of these actions, he holds an intense grudge toward Echidna, something that would even end up fogging his views of Eridna when they met, knowing that her name and mannerisms were a match for her creator’s.
At present, he is unaware that Echidna has taken on the form of Omega. Meanwhile, during her travels, she often finds herself thinking of and comparing her predicaments with that of Subaru.
Clind[]
Clind and Echidna's relationship was nothing more than that of distant acquaintances. However, according to the Greed What If side story, he seems to have a hostile view of Echidna, and he would attack Subaru for his association with her in said story. Whether this view is specifically to Echidna or to witches in general is unknown, and the cause of this view is unknown.
Priscilla Camp[]
Al[]
Although the author has stated that Echidna would have no interest in Al should they meet, it is revealed that Echidna is, in fact, Aldebaran’s teacher. As such, their past relationship is unknown. However, it should be noted that Al attacked Sphinx when she appeared in the form of the Witch of Greed, yelling Echidna's name all the while, implying his currently hostile relationship with the witch, and though he calls her “sensei”, he does so out of spite.
Lugunicans[]
Ryuzu Meyer[]
Ryuzu was taught by Echidna, they had a mutually respectful relationship. When the Sanctuary was under attack Ryuzu decided to assist Echidna, protecting the Sanctuary by sacrificing herself.
Others[]
Volcanica[]
While it's not known what kind of relationship the Divine Dragon and the Witch of Greed had, Volcanica was the one that kept Echidna's soul in her grave for four centuries as a deterrent to Satella.
Flugel[]
According to Alec, Flugel was part of the team that journeyed to save the world. Their relationship is unknown, but in Arc 4 in the Web Novel, she mentions Flugel while talking to Subaru. It can be assumed that at the very least, they had a relatively amenable relationship.
Alec Hoshin[]
According to Alec, he traveled together with the Witch of Greed and four others on a journey to save the world. The relationship between him and the Witch of Greed is unknown, but considering Echidna helped Houshin found the nation of Kararagi, it is likely these two were on friendly terms.