Nightfall is a version of Quinn from a parallel timeline. She is 20 years older than her main timeline counterpart.
In her timeline, she met and fell in love with Gary Goodspeed, who was as pilot in the Infinity Guard. Like in the main timeline, they met Mooncake and fought the Lord Commander, but Gary died when detonating an anti-matter bomb to close a breach to Final Space. At some point after his demise, Nightfall tried to commit suicide to reunite with Gary, but as she was about to throw herself from a rock, she was contacted by the Titan Bolo. He told her that she could change things by building a machine that traverses time. Thus, Nightfall build the machine and began her attempts to rewrite history.
She spend 20 years crossing the timelines trying to avoid Gary's death. However, no matter what she did, Gary died in each variation, most of the time by detonating the anti-matter bomb, but also frequently due to the Lord Commander killing him. In the timelines where the latter happened, Mooncake subsequently went berserk, and accidentally opened up a gate to Final Space which freed the Titans.
Nightfall appears for the first time in Chapter 2, where she is transported to the timeline in which the series takes place. After passing the defenses of the Galaxy One, she reveals herself to Mooncake, telling him that he shouldn't let Gary die because of him. She also gives KVN a chip of some sort, which she states he will need to save the Galaxy One someday. In Chapter 4, KVN uses this chip to reboot H.U.E. after the Infinity Guard remotely takes control of the Galaxy One in an attempt to arrest Quinn.
In Chapter 7, Nightfall formally introduces herself to the crew of Galaxy One after saving the Team Squad from an ill-prepared attempt to avenge the death of Avocato (who died in the previous episode due to the Lord Commander). After becomming acquainted with the team, she tries to prevent Gary from leaving the Galaxy One with Mooncake. She also warns Quinn against attempting to stop the breach (the same one that in her own timeline Gary closed) by herself, citing how these attempts are always doomed to fail. Quinn doesn't listen, so to save both Gary and the universe, Nightfall decides she has no choice but to kill Mooncake. Nightfall comes dangerously close to exterminating the gelatinous lifeform, only to be stopped by Gary and Quinn. To make matters worse, Little Cato and KVN attempt to steal her time machine to save Avocato, but end up activating the self-destruct. They are saved in time, but the machine is destroyed, robbing Nightfall of her ability to time travel. Quinn and Gary convince her to give Mooncake one last chance.
In "Chapter 8", Nightfall shows the Team Squad the way to Inner Space so they can talk to Bolo. After they learned from Bolo how to close the breach, Nightfall leaves, stating she is not needed anymore.
Nightfall is seen again in "The Toro Regatta". She seeks out the dying Lord Commander on the remains of his ship, and kills him, as she has done hundreds of times, but states that she sees that something is different on that occasion. She and Mooncake join Gary and the rest of the survivors on the Crimson Light in the search for the Dimensional Keys, which can free Bolo.
During the season, Nightfall tries to restart a relationship with Gary, but eventually has to accept that he is not "her" Gary, and that he only has eyes for the Quinn from this timeline (who sacrificed herself in "Chapter 10" to close the breach). In "The First Times They Met", she even tries to create an artificial Gary using her memories, but is forced to shut it down since the simulation is using too much of the Crimson Light's power, and thus endangers the crew. She then reveals to Gary that this is the first timeline in which Quinn closed the breach, since normally he is the one to make that sacrifice.
In "The Sixth Key", Nightfall ultimately decides to sacrifice herself to become the "sixth key" and free Bolo from his prison. In her final moments, Nightfall tells Gary to rescue Quinn and never let her go again.
Her facial appearance is the exact look of Quinn's, with only a small piece of technology on the right side of her forehead, and a gray part of her hair giving her a slightly different look. Nightfall also has several scars on the right side of her face. She also appears to have greyish blue eyes.
She wears mostly a bounty hunter-esc uniform, only to be used in order for her to aboard the ship.
Unlike Quinn, Nightfall is somewhat relaxed and is not as quite stubborn. However, she is shown to be protective of Gary, similar to Quinn, as she's been attempting to prevent the outcome of him dying for 20 years.
She is seen to be quite brash when it comes to doing necessary things on missions and adventures, and is known to use brute force if needed.
However, during the course of season two, she is seen sticking with the crew to ensure that the timeline will go as planned. During this time she grows close to the crew of the Crimson Light, especially with Ash Graven who she seemed to have developed a sort of parental bond with. This ultimately comes to a head in "The Sixth Key", where she sacrifices her life to free Bolo and so no other members of the crew would have to. Ash is seen holding onto her helmet at the end of the episode.
Quotes and catchphrases
- "Cause Einstein's a jerk."
- "Gotta say, Gary, I missed your wit."
- "I'm going to kill Mooncake, before he destroys all of us."
- "I've been back hundreds of times and the only option left is to kill Mooncake."
- “Something in our past, or maybe the past itself, connected us. And now I have to accept the possibility that there is no happy ending. That you and I are meant to be together, but never meant to be.”
- ”When you see Quinn, never let go.”
- ”Alright Mooncake, here we go.” (Last Words)