Echidna

Echidna is the Witch of Greed in Re:Zero − Starting Life in Another World. She is one of the legendary Witches of Sin from over 400 years ago, known for her extreme intellect, vast magical knowledge, and an insatiable curiosity for understanding everything in the world—particularly unknown phenomena.

She appears as a strikingly beautiful young woman with long snow-white hair, pale skin, and black eyes, often dressed in elegant black clothing. Her personality is highly intelligent and affable on the surface, but she is frequently described as emotionally detached or sociopathic by normal standards—she struggles to understand or empathize with others' feelings and views people (including Subaru) primarily as fascinating subjects for observation and experimentation.

In the story (especially Arc 4 of the anime/light novels), she interacts with Subaru in a dream-like realm called the Castle of Dreams/teaparty setting, where she offers guidance and expresses strong interest in his Return by Death ability, seeing it as an unparalleled tool for gathering infinite knowledge across timelines.

While she can come across as helpful or charming, her "greed" ultimately prioritizes acquiring information above all else, even at great cost to others.