The Flash season 7 honors several fallen heroes in the Arrowverse in the latest episode, reflecting on the people they have lost over the years. In most superhero shows, there comes a time almost every season when a series kills off a beloved character or two. As much good as the heroes do for the world, sometimes the cost comes with having to lose a loved one.
With a show like The Flash being in their seventh season, there are inevitably more losses involved. The longer the Arrowverse goes on, the more deaths will happen, as it represents the stakes these heroes have to face. Whether it's fighting someone like the Anti-Monitor, Reverse-Flash, or Prometheus, the danger wouldn't be felt if there weren't risks involved.
While they were able to finally create the Artificial Speed Force to get Barry his powers again, it came at a big cost. Nash Wells, who was holding every Harrison Wells in the entire Multiverse in his body, sacrificed himself in order to power up the Artificial Speed Force. Every incarnation of Harrison became part of Barry's new power source. His sacrifice had a huge effect on the team, as Nash and other Wells get a tribute in a new room that has become STAR Labs' own Hall of Mementos for other Arrowverse characters that they have lost.
Firestorm
While they died at different points, both Ronnie Raymond and Martin Stein - a.k.a. the original Firestorm - passed away several seasons ago. Firestorm was one of the first heroes that ever joined The Flash when Barry was first starting out, as both Ronnie and Martin were given powers by a particle accelerator explosion. Ronnie died in The Flash season 2 premiere when he, as Firestorm, sacrificed himself to close the singularity that they had opened. Martin died during the Crisis on Earth-X crossover after getting shot multiple times by a Nazi soldier. In order to save Jax Jackson, the new half of Firestorm, Martin cut the connection between them before passing away. Not only is Firestorm's first costume seen, but the quantum splicer is attached to it as well.
Captain Cold
Leonard Snart may have begun his run on The Flash as a villain, but he left the Arrowverse as a hero. Wentworth Miller's Captain Cold moved over to Legends of Tomorrow back in the first season as one of the team's wildcards, along with Heatwave who's still on the Waverider. In the penultimate episode of Legends of Tomorrow season 1, Leonard sacrificed himself to take down the Time Masters in the Vanishing Point. Miller has been back in the Arrowverse as a version of Snart before joining the Legends, a version from a while before he died, and as the heroic Citizen Cold from Earth-X. He also voiced an A.I. iteration of Snart that operated the Waverider from Earth-74 in Crisis on Infinite Earths. The original Captain Cold from 2016, however, has remained dead ever since, as his goggles can be seen in the hall.
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One of the biggest losses to hit The Flash was when Barry and Iris had to watch their future daughter Nora be erased from existence in the season 5 finale. After she and her father change the timeline to stop the villain Cicada, it also changed Nora's future. Because she had interfered with the past, it became a time travel consequence. A new version of Nora was alluded to be alive in the future as Wally West had seen her through the Speed Force before it died. Even if Barry and Iris see Nora again after she's born, it still wouldn't be the same one that they bonded with back in The Flash season 5.
Jesse Quick
Jesse Wells - a.k.a. Jesse Quick - is one Arrowverse hero whose current status is a big mystery, despite her costume being in the hall od dead heroes. When Earth-2 got destroyed during the Arrow season 8 premiere, Team Flash presumed later on that Jesse had died. Post-Crisis, Earth-2 is now the home of Stargirl, as well as John Wesley Shipp's Jay Garrick, meaning it's unclear whether or not Jesse lives again in that version of Earth-2. Since Violett Beane's CBS show got canceled last year, Jesse's return to the Arrowverse is hopefully coming up sometime this year, as it'd be weird to kill her offscreen. Stargirl season 2 could be where they officially declare if Jesse was reborn after Crisis, or if she maybe was revived on another Earth in the new Multiverse.
The Wells Memorial
During The Flash's run, the team has encountered various versions of Harrison. Some had longer runs while others appeared every once in a while in brief scenes. But for the team, they have specifically bonded with Harry Wells, H.R., Sherloque Wells, and Nash. The way the team honors those Wells are with certain items such as H.R.'s drumsticks, Sherloque's brandy bottle, Nash's bandolier (which Allegra now wears too), and Harry's glasses. Cisco Ramon has even made the Wall of Wells is nano-engraved so in case their timeline is ever rewritten, the names will at least never be forgotten in any new reality. It's bittersweet for The Flash to introduce this hall as it does honor the past seasons where these characters have lost allies and loved ones.
Even if the Arrowverse may never see alternative versions of someone like Firestorm, at least the series recognizes that they were there years ago. As heartbreaking as it's to see the tributes, this hall does maybe tease something that part of The Flash's mythology. This memorial room could be the beginning of what will be the Flash Museum one day since STAR Labs does, at some point in the future, turn into that. At least that was what was going to happen before Crisis on Infinite Earths. The museum might still happen on this Earth, but much later in the future than originally planned. Hopefully, it will be a long while before the Arrowverse loses another big player, including on The Flash.