WARNING: The following contains spoilers for Re: Zero - Starting Life in Another World, Season 2, Episode 20, "The Beginning of the Sanctuary and the Beginning of the End," now streaming on Crunchyroll.
Re: Zero's second season has leaned heavily into flashbacks, and while it certainly slows the story down, it has also opened up the backstory of several characters. The most recent comes in Episode 20 as Subaru tries to convince Roswaal to surrender, prompting a journey through the margrave's time with Echidna 400 years before the events of the series.
While Subaru's stance sees him supporting others and seeing the best in them, Roswaal takes the opposite approach and chooses to view their weaknesses. Roswaal refuses to change his mind, continuing to believe that everything he's done until this point -- through his love of Echidna -- served a greater purpose and can't be undone so hastily. How Subaru and Roswaal's conflict will end depends entirely on Emilia, who Roswaal is convinced will fail, and Subaru trusts wholeheartedly.
Echidna Saves Roswaal
When he was younger, Roswaal suffered from an excess of mana stored in his body, which he didn't understand until he met Echidna -- who kissed (yes, kissed) the blockage out of him. From that point on, he became Echidna's student and developed romantic feelings towards her. The flashback shows Roswaal, Echidna, Beatrice and the original Ryuzu Meyer all together as a pseudo-family. However, their collective union shared a single, central goal of creating the Sanctuary.
As has become a theme in Re: Zero Season 2, these happy moments are often brief and fleeting, quickly giving way to looming darkness. That harmony which was seemingly nestling itself into the group is shattered by the approach of a mysterious man named Hector. To protect themselves -- and their new community of demi-humans -- Echidna and Roswaal have been tirelessly working on the barrier to surround the Sanctuary. Unfortunately, it requires Ryuzu's Od, or life energy, to fully power it.
Roswaal's Determination and Ryuzu's Sacrifice
Hector -- also known as the Devil of Melancholy -- has an unknown history with Echidna, but it's clear that they aren't friendly towards one another. Roswaal tries to buy time for Echidna to prepare for Hector while Ryuzu heads towards the crystal we've seen her trapped within in present day. Roswaal is violently pummeled by Hector's attacks -- which aren't too dissimilar from Betelgeuse's Unseen Hands --, but he bravely continues stalling for Echidna's sake.
Meanwhile, Ryuzu and Beatrice enter the crystal's chamber. Beatrice is initially unaware that the crystal will serve as the catalyst to form the Sanctuary's barrier using Ryuzu's Od as the core. To protect everyone, Ryuzu knowingly sacrifices herself so all of her friends' hard work won't go to waste, and she can help protect Echidna. Ryuzu's sacrifice significantly impacts both Roswaal and Beatrice. Even now, Roswaal continues to hold the Sanctuary and his feelings for Echidna in high regard.
Emilia Will Be the Deciding Factor
Back in the current day, Subaru once again asks Roswaal to surrender. However, Roswaal refuses and points to his 400-year dedication as unshakable, despite Subaru's recent success of bringing Garfiel to his side. Roswaal tries to insult Garfiel's convictions after he had spent years being hostile towards outsiders and wanting to preserve the Sanctuary. Along with finally facing his past, Garfiel also explains that he joined Subaru because he values Garfiel's strength, while Roswaal kept him weak.
Subaru and Roswaal's differing philosophies are highlighted in their perceptions of people -- namely Emilia and Garfiel. Where Subaru sees caring about something deeply, or for a long time, as a strength, Roswaal views it as a weakness where someone clings to one thing without ever fulfilling their desires. For over 400 years, Roswaal has persevered for Echidna's sake and won't surrender because he can't see beyond his stubbornness, confident that Emilia will fail and make way for his mysterious plans.
Roswaal's confidence that Emilia will fail remains his "advantage," and while he's unaware of her recent success in the Witch's Trial, he remains resolute. Despite Subaru's best efforts, it looks like he hasn't yet gained another ally in his quest to liberate the Sanctuary. Still, Roswaal's flashback only begs more questions regarding Echidna's fate, his multi-colored eyes and what happened to the mysterious Hector.