Contains spoilers for “Agatha All Along” Season 1, Episode 4 — “If I Can’t Reach You / Let My Song Teach You” 

The supernatural “Agatha All Along” puts Kathryn Hahn’s delightfully evil “WandaVision” antagonist front and center, but it also features plenty of other interesting characters. One of the most fascinating is Rio Vidal (Aubrey Plaza), who may turn out to be either Agatha Harkness’ (Kathryn Hahn) greatest ally — or her deadliest enemy. Fans may have thought that it’s strange that an actor of Plaza’s talent and stature would portray a seemingly random witch, and from the looks of it, said fans are right. Increasingly, it seems that Rio Vidal is more than meets the eye, and “If I Can’t Reach You / Let My Song Teach You” continues to heavily hint that Rio’s true identity might be far … deadlier than just a powerful witch with a strange fascination toward Agatha Harkness (Kathryn Hahn).

Let’s assume that all the clues about Rio are indeed correct and she’s the Marvel Cinematic Universe’s personification of Death. If this is true, hey, amazing casting! However, it also raises a very particular question: Why is Rio unable to kill Agatha? This seems strange, especially if death is her entire deal. Let’s take a look at the available evidence of Rio’s true nature and the possible reasons behind her odd relationship with Agatha.

The biggest and most tangible clue that Rio Vidal is far more than a witch is her spoilery Funko POP figure, which casually calls her Death in lieu of her supposed name. While that’s a pretty hefty clue, “If I Can’t Reach You / Let My Song Teach You” also offers its share of hints that Rio has at least a connection to death. She answers to the green witch summon spell by climbing from Mrs. Hart’s (Debra Jo Rupp) grave, with the implication that she may have hijacked the corpse and molded it into her own image … which just so happens to bear some resemblance to the Asgardian death goddess, Hela (Cate Blanchett). She’s also the only member of the coven who’s not affected by the curse and the only one whose attitude toward the Witches’ Road is amusement instead of fear.

When Teen (Joe Locke) is about to die, the panicked Agatha seems to quietly plead with Rio not to take him away. Later, Rio tells Agatha that Teen – whose identity has been Funko POP-spoiled as Wanda Maximoff’s (Elizabeth Olsen) son Wiccan — is not her lost child. This shows that she has access to the kind of information Agatha and other coven members can only dream of … and thus is levels above them.

On the other hand, Rio herself is quick to label herself the Green Witch in a cool demonic voice, presumably meaning this in the same sense as Wanda is the Scarlet Witch. This could simply be a fun alias she creates to ease her way into the coven. On the other hand, if she’s serious, this may potentially mean that she’s roughly as powerful as Wanda — though probably not quite as powerful as Death itself.

Going with the “Rio is a personification of Death” theory, let’s look into the various reasons she might nevertheless be unable to kill Agatha. The first of them is simple: She’s not the actual Death, but rather her agent or aspect — a grim reaper instead of the Grim Reaper, if you will. Since Rio seems to be affiliated with witches and witchcraft, such a role would effectively make her a death witch. This, in turn, could mean that she’s still bound by the witch community’s internal rules. As “Agatha All Along” Episode 1 establishes, witches can’t kill other witches, which would be a pretty simple explanation for Rio’s inability to take Agatha’s life.

There are also rumors that Rio isn’t a direct adaptation of any single character, but instead combines aspects of several Marvel characters. Considering that she’s far more animated and mischievous than traditional comic book versions of Marvel’s Lady Death, this seems like a very possible potential explanation to her as-yet unrevealed intricacies.

Despite early rumors, Mephisto never appeared in “WandaVision,” but the Marvel devil’s fingerprints are all over “Agatha All Along.” He actually gets a namedrop in Episode 3, and it’s heavily implied that Agatha sacrificed her son in a deal with him to gain her powers — and possibly other little benefits, such as some form of immortality. After all, Agatha has been around since the 17th century, so at the very least, it seems safe to suspect that Death is not her greatest fan.

With devil imagery aplenty in Episode 4, the show isn’t exactly shying away from teasing Mephisto’s influence, so this seems like a fairly plausible theory. As an old-school Salem witch with a relentless thirst for power, Agatha certainly may have stooped low enough to make deals with the devil. Rio/Death’s frustration over her inability to take Agatha’s life would also explain her initial hostility toward the witch, from physically attacking Agatha to sending the Salem Seven after her.

Intriguingly, this would effectively make the pair’s tender moments in Episode 4 a carefully choreographed display of barely-contained hostility, something that has been brewing for so long that the pair has begrudgingly become affectionate toward each other. With actors of Kathryn Hahn and Aubrey Plaza’s caliber on the job, should this prove to be true, the approach could yield some truly delightful scenes down the line.

If Rio is Death, this one isn’t as much a theory as it is a confirmation that she refuses to kill Agatha out of love. After all, it’s already heavily implied that she loves — or, at least, used to love — the witch. In Episode 4, the coven is sharing their battle scars around a fire, and Rio shares a story about a metaphorical scar she received when she loved someone so much that she couldn’t hurt her, even though it was her job. At both the beginning and end of the tale, she glances at Agatha, who looks uncharacteristically lost in thought as she listens.

Combine this with the pair’s obvious chemistry and the near-kiss at the end of the episode, and there’s little question that there are feelings involved. Judging by the fact that Agatha casually points out that Rio doesn’t actually have any scars, she’s either fully aware of her true identity as Death … or she simply knows Rio’s body well enough to confidently comment on its scar-free status. Either way, it’s clear that the pair has a history, and it’s all but explicitly stated to be a romantic one.

The many Easter eggs in “Agatha All Along” episodes are custom-designed to keep the fans guessing, so there’s a good chance that we still have to wait a while before Rio Vidal reveals her true nature. Still, as it stands, all signs seem to point toward the Death theory. The real question seems to be just how things started out between her and Agatha … and how they’ll play out by the time “Agatha All Along” Season 1 ends.