Reading Steiner activated and brought Okabe back to the Alpha Timeline where Kurisu lives and Mayuri is dead. Yep, after 7 episodes being reminded of how no Kurisu is suffering for Okabe and Maho, now we see how Mayuri's death affected Okabe and all his friends for the worse.
We see Mayuri's friend (who replaced Mayuri at the maid cafe with Feris) breaking down just from remembering Mayuri, Daru getting angry at Okabe when the latter brought up the possibility of Mayuri living in another timeline while the former was reminded of how he had a role in Mayuri's death, and Okabe standing in front of Mayuri's grave from morning until night (from what Kurisu tells us).
Okabe becomes even more traumatized than he already is seeing a world without Mayuri and knowing one timeline has one girl he loves dead while the other he's childhood friends with alive (Beta line) while the other timeline is vice versa (Alpha line). There's just no escaping the pain of losing the ones he closest to. The scene when he visits Mayuri's grave and reaches out to the sky, imitating her signature stargaze reach, as he cried was so beautiful and heartbreaking. The cinematography was also fantastic, and they really portrayed it in a way like Mayuri came down from heaven to give Okabe a handshake.
The emotion from Mayuri's loss is one part that made this a great episode, but the other half was a reminder why Kurisu is best girl!
She realizes the Okabe that just arrived in the Alpha Timeline came from the Beta Timeline. Remembering how distraught Okabe was over Mayuri's death in the Alpha timeline just from seeing how Okabe is traumatized again, she cannot bear to see him in the state he is now. From the time prior, we learn that she rebuilt the Phone Microwave time machine from scratch to bring Okabe to the other timeline.
Okabe is skeptical and sad; the loss of Mayuri is too much for him, but he also does not want to go back to a timeline where Kurisu is dead. To Kurisu, she doesn't mind. She willingly accepts dying in another timeline just so she doesn't see Okabe being distraught anymore. Yep, Kurisu still loves him! She even KISSES him right before she sends him back. Man, the episode was just pulling my heart strings at that point!
Then we learn the events leading up to Kurisu running into Okabe's lab on the last second in episode 22 of the original Steins; Gate where he is sent back just as she is about to confess. Turns out they sent a D-mail to her with the message "Don't come in." Her reading the message bought Okabe enough time to press the button to trigger phone microwave; otherwise, if it wasn't for that message, Okabe wouldn't have pressed the button upon hearing Kurisu say "I love you."
This was such an awesome and emotional episode overall!