Echidna - Re:Zero
Name: Echidna
Age: 19 (spirit), mid twenties (actual body)
Race: Unknown (humanoid looking)
Gender: Female
Birthday: 24th of January
Voice Actors: Not yet revealed
Echidna is the Witch of Greed who survived for a long time in her Sanctuary even after Satella killed all of the Witches of Sin. Echidna is a woman described as beautiful with long snow white hair that extends past her waist and black eyes. She wears a hairclip in the shape of a butterfly wing over the left ear. She typically wears a full length black dress that is fairly modest looking and with white trim and accents. She was also once shown wearing a Japanese school uniform when she showed up in Subaru's memories of his life in Japan. Echidna is a fairly amiable person whose interest lies in intellectual pursuits. However, she is also somewhat of a sociopath who is unafraid of lies and deceit so long as it serves her goals of obtaining more knowledge.
History
Before the events with Satella and a long time ago Echidna was an intellectual who lived on a floating island of her own creation. According to her, royals near and far would seek her out for her great wisdom during her lifetime. She thought that it would be easy to take control of the world, but instead dedicated her efforts into protecting things instead. Despite all of her talents she was still unable to achieve anything significant on her own which made her realize her own powerlessness. She worked through her despair and sought others who would share in her interests and desires.
At some point she established her Sanctuary where she continued with her experimentations. It is here that she met with the first Roswaal, created Puck, Beatrice, and Lewes Meyer. She experimented with immortality though that particular pursuit was cut short due to events with Satella. It is still unclear the extent to which Echidna's influence has shaped the events of the story, but she much of her legacy continues to affect the current events of Re:Zero such as the gospel book that was in Roswaal's possession or the incredibly powerful metia that Felt has used. Before Satella was able to kill the other Witches, Echidna took in their souls (including Satella's) which she keeps to this day.
Regardless, Subaru first meets Echidna during the events of Arc 4 when he enters her graveyard without her blessing. She is fascinated by his Return by Death ability for since it allowed Subaru to obtain information from multiple perspectives and timelines. She continuously aided him until he rejected an offer from her (on the advice of the other Witches) to form a contract. This caused her to rescind her blessing though Subaru was still able to solve the crises around the Sanctuary.
Just before the full resolution of those events, Echidna absorbed the soul of the Lewes Meyer Omega clone and used that to transfer her own soul into the original body of Lewes Meyer. She then left to wander the Kingdom of Lugnica without the knowledge of any of the heroes.
Relationships
Satella - Satella is the one who caused Echidna's death some 400 years ago. While the other witches only hold resentment for the Witch of Envy personality Echidna also hates Satella herself.
Minerva - Among the Witch souls in her, Echidna gets along best with Minerva for their shared goal of taking care of others.
Roswaal Mathers - Echidna saved the first Roswaal and helped to restore his defective gate. After her death, he began obsessing with reviving her and has possessed his descendents ever since in order to accomplish this goal.
Lewes Meyer and Beatrice - Echidna created the two around 400 years prior to the start of the story. They both see her as an actual mother and refer to her as such.
Natsuki Subaru - Subaru's Return by Death ability facsinates Echidna and she went out of her way to help him. Eventually she offers him a contract though he rejects the offer after being advised by the other Witches that Echidna wasn't being wholly forthcoming.
Emilia - Echidna is apparently quite connected to Emilia and bears a large amount of animosity for the half elf. She apparently has knowledge about Emilia's parents.
Abilities
Intelligence - Echidna's defining trait and driving force in life is the pursuit of intelligence. Her plans, abilities, and capabilities make it hard to fully understand everything that she has done and accomplished behind the scenes.
Catalyzing Body Fluids - Echidna fed her body fluids to Subaru which caused the Witch Factors within him to stabilize.
Authority of Greed - As the Witch of Greed, she has the capability of using the Authority of Greed.
Magic User - Echidna is extremely skilled in magic and is also able to use all six elements.