Warning: Contains spoilers for Marvel’s What If…? episode 9.
The What If…? season finale introduced an iteration of Gamora to the Guardians of the Multiverse and gave her Thanos’ Avengers: Endgame armor and sword. Gamora’s possession of Thanos’ equipment was originally teased in the original What If…? poster. However, audiences have had to wait through the whole series to find out how she would have acquired these items from her father.
Thanos’ battle armor is an adaptation of his appearance in the comics. In the main MCU timeline Thanos is seen wearing the armor during his massacre of the Korbinites, when Ronan the Accuser confronts him in Guardians of the Galaxy, and during his assault on the Statesman that held the surviving Asgardians in Avengers: Infinity War. As he claims the Space Stone from the Tesseract, he removes his armor, highlighting that with the power of two Infinity Stones the armor is less necessary. In Avengers: Endgame, the armor is used as a scarecrow at his retreat on the Garden before the alternate timeline Thanos appears wearing the same armor for the final battle.
What If…? introduces the Guardians of the Multiverse version of Gamora (Cynthia McWilliams) in a brief scene where The Watcher (Jeffrey Wright) announces that she is chosen and she is already wielding Thanos’ armor and double-bladed sword. While What If…? doesn’t explicitly state why she has these items, a lot can be inferred from a single line from the Watcher and other plot elements that surround the character. The Watcher refers to Gamora as “destroyer of Thanos,” combined with her introduction showing her and Tony Stark (Mick Wingert) melting down an Infinity Gauntlet and Gamora possessing an Infinity Crusher for destroying the Infinity Stones, it becomes pretty clear that in this timeline Gamora killed her father and claimed his armor and weapon.
However, with what is known of the Gamora of the main MCU timeline, it is not entirely clear why this Gamora would use Thanos’ armor and sword. In the main MCU timeline, Gamora holds her father in contempt and would rather distance herself from him than take on his mantle. However, as The Watcher seems to credit Gamora alone with Thanos’ death, it is possible that she defeated the Titan in more direct combat by herself and her new weapon and armor serve as warrior symbolism of her victory over him. Alternatively, as The Watcher also calls her “survivor of Sakaar,” the home of the Grandmaster’s tournament, it is possible that the use of this equipment was instrumental to her survival and now holds special relevance to her.
It was not the showrunner’s intention for Gamora to get such a rushed introduction. What If…? season 1 was originally intended to include 10 episodes with the missing episode being a lighter, comedic episode in a similar vein to “What If… Thor Were an Only Child?” This episode would presumably have covered the introduction of Gamora and this universe’s Iron Man in a Sakaarian adventure. This episode is expected to now be included in What If…? season 2, so viewers may yet get a more complete explanation of why Gamora has Thanos’ Avengers: Endgame weapon and armor. However, for now, the implication remains that this alternative version of Gamora is the only one to overcome her genocidal adoptive father and inherit his weaponry.