WARNING: The following contains spoilers for Re:Zero - Starting Life in Another World, Season 2, Episode 12, "The Witches' Tea Party," now streaming on Crunchyroll.
The mysterious Witch of Greed Echidna has finally given Subaru some context for all of her weird machinations, though perhaps he would have been better off not knowing. Behind her smile, the Witch embodies her namesake entirely as she offers Subaru a rather one-sided proposition following a disturbing revelation regarding Return by Death.
After a bit of exposition where Subaru recounts his experience with Roswaal -- namely, that the patriarch of the house is aware of Return by Death and is exploiting it for some unknown goal -- he does the only logical thing by returning to the Sanctuary to consult Echidna. As he enters the temple wherein the Trials take place, Subaru asks again to be invited to Echidna's tea party only to be rendered unconscious.
Suddenly a vision of a dead Subaru appears, his limp body bleeding out beside the presumably dead Rem as Emilia and Felis attempt to resurrect him, to no avail. The vision is the first time Subaru witnesses the aftermath of Return by Death, a glimpse into an alternate world presented by a mysterious voice telling him to behold the unthinkable. Again the voice echoes through the chamber and Subaru returns to another post-Return by Death reality where he'd been murdered, leaving behind his mourning allies. When he awakes, Subaru is thrust yet again into an alternate reality where his death has a serious effect on those who care for him -- until he reaches one where Puck, standing in a frozen wasteland, is ready to destroy the world.
Puck, who had previously promised to destroy the world should anything happen to Emilia, is in his savage-beast form when he is confronted by Reinhardt. Just as the confrontation escalates towards brutal battle, Puck coldly tells Reinhardt that he'll only ever be a hero. As Reinhardt lifts his Dragon Sword, Puck is completely destroyed. The Dragon Sword is said to only work at its full power for worthy opponents, meaning Puck was truly ready to total the world.
When Subaru wakes again, he's subjected to a montage of worlds in which he died either by his own hand or by others'. When he begs for it to stop, Rem appears. She offers to console him and the battered Subaru obliges before realizing that she couldn't possibly be there. Lucky for him, the illusion is shattered and the Witch of Lust appears in her stead. Using a power called “Faceless Bride,” Lust appears as whatever her target desires the most -- and also forces the person to forget to breathe, suffocating them. Echidna steps in before that can happen, however, and Subaru is thrust into her Tea Party.
Righteously upset, Subaru asks why he was shown these awful visions and bluntly Echidna tells him that they may actually exist in, well, another world. This flips the entirety of Re:Zero on its end and gives the meaning of “Starting Life in a New World” an entirely different context. If Subaru is actually leaving behind the worlds he physically dies in, that means he's also leaving behind countless versions of his allies to mourn and suffer without him.
But there's no time to consider the consequences as Echidna presents Subaru with a contract. By allowing Echidna to “take part” in his Return by Death, she will assist him in working his way toward a “happy ending.” Before he can agree to the somewhat loose terms, the Witch of Wrath interrupts the proceedings to inform Subaru that Echidna isn't being honest regarding the terms, specifically, the portions of the agreement that would be bad for him.
When Lust arrives, even more is revealed regarding Echidna's true intent: she wants a taste of everything Subaru uncovers. When the Witch of Sloth appears, she notes that the promise would be preceded by “in the end,” whenever that may be. As the rest of the Witches appear, Echidna reveals that while Subaru would receive the “best possible ending,” he may not take the “best possible path.” Before a decision can be made, the Witches shudder in unison as the final and most powerful of them all appears. Satella, the Witch of Envy, has arrived and the others are not happy to see her.
With the latest revelation regarding Return by Death on his mind, Subaru's choice of whether or not to agree to Echidna's terms may very well rest on his ability to live with the guilt of abandoning his friends to a world without him.