The second ending, Stay Alive, which is sang by Emilia (Rie Takahashi). Both the lyrics and the pictures show us Emilias lonely life after returning to the Manor without Subaru.
Oh, Stay... Alive- I wonder what you're thinking right now... I haven't cried yet, But I do feel lonesome all by myself...
Requiem of Silence is this in distilled pure adulterated form, to the point where it seems to be the theme of the end of a Greek or Shakespearean Tragedy then an anime.
Arc 1 | Season 1 Episodes 1-3 | Light Novel 1
Episode 1: From Emilia's perspective, she just made a new friend who doesn't hate her because of the prejudiced against half-elves and now both have been crudely disemboweled and left for dead. Double as Heartwarming, since even in agony of death he still attempts to reach out to her and grab her hand, which we see in the first ending, Styx Helix, she recipricates.
Arc 2 | Season 1 Episodes 4-11 | Light Novel 2-3
Episode 7: Subaru finally finds out that Rem, someone he believed was his friend was the one who'd been killing him, and had hated him from the very beginning. In the end, when his death draws near he can do nothing but sob his eyes out and scream how much he'd grown to care for the twins in futile resistance. Rem either thinks he's lying or has gone mad and simply watches his execution at the hands of Ram.
Rem: My sister is far too kind.
Later in the episode, after surviving the fourth night thanks to a contract Beatrice formed with him, Subaru finds out the next morning that Rem died in his place, causing Ram to grieve for her and chase after Subaru in revenge.
Episode 8: Subaru wakes up in a new loop with the resolve to befriend Ram and Rem. He works incredibly hard to ingratiate himself to them, and he manages to at least win their favour. Despite this, the incredible psychological toll it's taking on him rears its head, and nearly causes the poor boy to break- until Emilia offers him a shoulder to cry on, and Subaru takes her up on her offer, bursting into tears. He cries so hard he actually passes out from exhaustion.
Emilia: The version of me that lives within you must be amazing. She understands all of your thoughts. Even if you don't explain them to her. She can feel all your pain. All of your sadness, as well as your anger as her very own... I can't understand if you don't tell me, Subaru.
Episode 14: Near the end of the episode, Rem decides to go on ahead to the mansion because she wants Subaru to stay safe. When Subaru chases after her, he arrives late to the aftermath of horrific battle that killed the mansion's residents along with Ram, Rem and Emilia. Subaru goes down into the frozen bowls of the mansion in search of answers, only to freeze to death.
Episode 15: Subaru once again Late to the Tragedy, just freed from the chains he was left in by the Witch's Cult carrying Rem's body after hearing her Dying Declaration of Love and dying on his arms. As he approaches the village, he sees the bodies of everyone he failed to save in a frozen wasteland that used to be his home. He then dies to Puck, with the most tragic music playing the entire time. In addition the blood red credits giving the feeling of an ending to an tragic war movie. If it wasn't for Subaru's Return By Death, it would have been the most tragic Downer Ending of all time.
Episode 18: Subaru, faced with constant failures and sacrifices, chooses to run away from his problems entirely. When Rem tries to talk him down from that decision, he goes on a prolonged Heroic Self-Deprecation rant about how he had waste his life up to that point and his existence in the world he's been brought to is meaningless.
Subaru: Before I got into the situation that led me to all of you, do you have any idea what I did? I did nothing. I've never done a single thing. I had all that time, all that freedom... I could have done anything, but I never did a thing! And this is the result! What I am now is the result! All of my powerlessness, all of my incompetence, is the product of my rotten character. That's right. I have no character. Even when I thought I could live here, nothing changed. At heart, I'm just a small, cowardly, filthy piece of trash, who's always worried about how others see me. And nothing... Nothing about me has changed! ...I absolutely hate myself...
Subaru's words can come out as incredibly harmful for Rem. Here's the man she considers her hero reducing himself to an useless mess who has yet to accomplish something that justifies his existence. It's almost as if his success at saving Rem in the past was meaningless for him.
Subaru: Yeah, they're right. No one ever needed me.
Rem: (shaking her head) That's not-
Subaru: It is true!
Episode 21: Wilhelm's declaration of love toward his late wife after killing the White Whale, which is interjected by a very touching flashback scene. We can say that Manly Tears were shed for that moment.
Episode 23: After all the effort Subaru and his allies made to defeat Betelgeuse's fingers, Subaru is suddenly possessed by Betelgeuse due his compatibility with him due the Witch's miasma and starts to lose his mind to him. In a desperate effort to regain his sanity, Subaru pleads to Felix and Julius to kill him before it's too late and eventually they do. The reaction of both Felix (who even starts to cry) and Julius is heartbreaking, especially for Julius, who recently made peace with Subaru after their previous resentment for their one-sided duel in the royal palace episodes ago.
To make things more painful, Subaru was just about to meet Emilia again for the first time in that loop after their breakup in the 13th episode, and he dies without even managing to say one word to her.
Episode 26: Brimming with triumph after defeating Betelgeuse and confessing to Emilia, it all begins to unravel with two words:
Emilia: Who's Rem?
To further elaborate, after the battle with the White Whale, everyone who was too injured to fight the Witch's Cult was ambushed and Rem ended up in a fight against two other archbishops. She ended up in a coma with no one remembering her. Despite having finally beaten back the Witch's Cult, Subaru follows through with killing himself only to learn that his save point updated meaning that he is not capable of saving her.
Even worse in the light novel. After Subaru comes back to the mansion to find Rem in a coma, he instantly slits his throat. He wasn't even aware he was doing it at the time; it was just a spontaneous reaction. Unlike the anime, no build up, no hesitation.
Arc 4 | Season 2 Episodes 27- | Light Novel 10-
Subaru's second Trial. After he had stumbled into the sanctuary it activates again and begins showing him visions of the worlds he's left behind. In these visions, all he sees are people mourning his death but the most noteworthy are Emilia's and Wilhelm's:
In the vision from after Subaru killed himself to try and save Rem, Emilia is grieving and Wilhelm after recovering from shock is trying in vain to resuscitate the body to no avail.
In the vision from his death via Julius, he has yet to have his Love Confession with Emilia so she does not know the meaning behind his actions. Then Wilhelm comes and upon seeing Subaru openly weeps upon seeing his fallen comrade. Ferris and Julius are in poor shape too.
The cherry on top? There's nothing to indicate that these events and more did not happen after the previous loops. It is entirely dependent on how Subaru's Witch Factor works and the only one who could answer his questions would be the person who gave it to him, the Witch of Envy.
Chapter 119 of the web novel is no picnic, as it shows a young Emilia and Fortuna about to separate.
Please listen to me, Emilia. Everything's okay. I'll come... yes, I'll deal with this quickly and come right back. So please stay hidden here while I'm doing that. Please. No! I don't wanna! Mother Fortuna, you're making a face like Juice did! Like Juice did, what're you gonna do! L-leaving me, what're you... going to... Emilia's little hands cling desperately to keep her mother from escaping. Fortuna should be easily capable of untangling herself from a child's grip if she wanted to. Her reasoning for not cruelly untangling herself from Emilia's hands is evidenced by her amethyst eyes as she gazes at Emilia. Fortuna is Emilia's mother. So she cannot bat away the hands of her crying, clinging daughter. Don't leave me! Let me be with you! I won't tell lies any more! I won't break promises! I'll be a good girl, I'll be a good good girl... so don't leave, me... Emilia... Emilia, Emilia, Emilia! Not wanting to be separated from her mother, and willing to sacrificing everything so that she does not have to separate from her mother, Emilia shrieks. Fortuna, her expression collapsing with emotion, hugs her daughter tight. If she does not press her daughter's face to her chest as she is, she'd see it.
How Geuse became the insane man he is today, according to the flashback with Emilia. To see someone who went from a caring person and father figure to... well, Betelgeuse, is heartbreaking.
Subaru somehow loses his memory of his entire time in the alternate world. Makes even worse that he is the only person who remembers Rem following her coma, now no one remembers her.
According to the official Q&A, Subaru's parents are still looking for him in his old world. His mother is getting depressed about their son's disappearance, and though his father tries to comfort her, it's not working nearly enough as it should.