Laurel goes through all the five stages of grief in this episode: denial (she refuses to believe Earth-2 is gone and tries to get back there), anger (at Oliver and at Chin), bargaining (mingled with denial; she assumes the breach device is broken and tries to get it fixed), depression (her Survivor's Guilt), and finally, acceptance (joining Oliver to help prevent the Anti-Monitor from destroying more worlds).
Laurel discovering that Earth-2 no longer exists is reminiscent of a similar scene in the original Crisis on Infinite Earths story, where Jay and Wally discover that Earth-2 no longer exists.
Lyla Michaels (codenamed "Harbinger") seemed to be an original character who just happened to share the name of a character from the ''Crisis on Infinite Earths" comic. But this episode reveals that she is in fact an adaptation of the Harbinger character from the original story, and like her comic-book counterpart, she's working for the Monitor. In the comics Lyla is Mar Novu's adopted daughter.
Similarly to the previous episode, this episode also has many references and callbacks to previous episodes, mainly from flashbacks of Season 3. When Diggle and Oliver goes to a cafe, the shots have very much resemblance to the once in The Calm (2014), where Oliver tries to send email to his his mother. When they get access to A.R.G.U.S. computer, Oliver also says how it would've been nice to know that ten years ago. China White and Alpha-Omega virus return as the main plot in this episode. Tatsu mentions how she became vigilante in Hong Kong, after Crescent Order exiled her, due to her giving Nyssa al Ghul the Lotus, referencing the events of Unchained (2016). When arguing about using the Alpha-Omega virus as bait to lure Chien Na Wei, Tatsu reminds Oliver how Maseo made the same gamble, referencing to the events of Midnight City (2015). Chien Na Wei talks about their previous fight to Tatsu; that happened in The Climb (2014) and resulted in Tatsu's loss. Tatsu and Oliver talk about Akio's death that happened in This Is Your Sword (2015), which is the main reason Tatsu became vigilante in Hong Kong after her exile. Tatsu also reminds Oliver how grief and anger made him torture General Shrieve for hours, referencing what happened in My Name Is Oliver Queen (2015). Oliver mentions that him and China White have been enemies from the start. China White was the first recurring villain Arrow had, first appearing in Honor Thy Father (2012). This could also be reference to China White being the first enemy that Oliver meets again from his 5 years of absence.
Tatsu now uses two katanas at once.