Sacrifice of Gamora

"In order to take the stone, you must lose that which you love. A soul for a soul."

- Stonekeeper

The Sacrifice of Gamora was sixth stage in Thanos' plan to obtain all six Infinity Stones. After discovering that Gamora found the location of the Soul Stone, he kidnaped her and forced her to reveal the location. The two went to Vormir where they were approached by the Stonekeeper who informed them that in order to retrieve the stone, a sacrifice must be made. Thanos then sacrificed his adopted daughter and in return obtained the stone.

Background
"If things go wrong, if Thanos gets me, I want you to promise me, you’ll kill me."

- Gamora to Star-Lord

An adopted daughter of Thanos after the Massacre of the Zehoberei, Gamora was asked by the Mad Titan to locate and retrieve the Soul Stone, which Thanos needed to complete his Infinity Gauntlet and fulfill his project of exterminating half of all life in the universe. Gamora successfully retrieved a map leading to the Soul Stone on Vormir. However, she chose not to reveal her achievement to Thanos, instead pretending that she had failed and burning the map.

However, Thanos was not fooled by Gamora's lies and knew that she had found the location of the Soul Stone. Some time after Ego's Expansion, Gamora's sister Nebula infiltrated the Sanctuary II, and attempted to assassinate Thanos, only to be thwarted and kept in custody. Probing Nebula's cybernetic memory banks, Thanos's suspicions were confirmed, that Gamora knew of the Soul Stone's location and had secretly admitted it to Nebula.

Having decided to move further in his quest, Thanos lured the Guardians of the Galaxy, to which Gamora belonged, to Knowhere, where he took the Reality Stone, and ambushed them. Before Star-Lord could kill Gamora to prevent the knowledge of the Soul Stone falling into his hands, Thanos captured Gamora, taking her back to the Sanctuary II.

Despite Gamora's attempts to lie, Thanos revealed that he knew Gamora had found the Soul Stone, through the memories of the captive Nebula, and began to brutally torture her to force Gamora to reveal its location. Unable to let her sister die, Gamora eventually caved in, and revealed the location of the Soul Stone to Thanos, on Vormir. To confirm this, he and Gamora left for Vormir, with Thanos threatening to kill Nebula if Gamora was found to be lying.

Sacrifice
"No. This isn't love." "I ignored my destiny once, I cannot do that again. Even for you. I'm sorry, little one."

- Gamora and Thanos

Upon arriving on Vormir, Thanos and Gamora found themselves in a desert surrounded by pools of water under a dark sky and eclipsed sun. The two stood at the base of a great mountain, atop which stood a tall altar. As they scaled the mountain towards the altar's entrance, they were welcomed by the Stonekeeper, a cloaked, ethereal wraith and the guardian of the Soul Stone, who greeted them by name. When Thanos questioned him as to how he knew their identities, the Stonekeeper informed them that he was cursed to know all who journeyed to the Soul Stone's altar. However, when Thanos demanded the whereabouts of the Stone, the Stonekeeper warned him that the Stone itself comes at a terrible price, that none are prepared to give. Stepping out of the shadows, the Stonekeeper revealed himself as the banished, former leader of HYDRA, the Red Skull.

As the Stonekeeper led Thanos and Gamora deeper into the altar, he explained how he came to become the Soul Stone's guardian - a lifetime ago on Earth, much like Thanos, he too originally sought the Infinity Stones, even once wielding the Space Stone in his hand. However, the Stone judged him unworthy of its power, and banished him to Vormir to become the eternal keeper of the Soul Stone. As he concluded his story, he finally brought Thanos and Gamora to a sacrificial cliff at the end of the altar.

The Stonekeeper informed them that in order to obtain the Stone, one would have to sacrifice the one being they love most to the cliff, astonishing Thanos. This revelation greatly amused Gamora, who taunted her adoptive father, believing that he loved nothing and this was the universe's way of ironically punishing him for his bloody quest of destruction. Silently, Thanos turned around, revealing that he was crying. Believing he was weeping due to his failure, Gamora continued to taunt him.

However, the Stonekeeper saw his true intentions, informing Gamora that Thanos was in fact weeping for Gamora, as he truly loved her as a daughter, and was heartbroken that he had to sacrifice her to get the Soul Stone. Genuinely surprised and in disbelief, Gamora could not comprehend that Thanos ever showed genuine love for her. However, upon realizing it was true, Gamora quickly took her switchblade from Thanos's belt. Drawing it, she attempted to kill herself, only to be thwarted by the Reality Stone, opening her hand to reveal only bubbles.

Tearfully, Thanos apologized to his daughter for what he was about to do, before grabbing her arm and dragging her screaming, towards the edge of the cliff. Despite his reluctance and her frantic screams, Thanos threw Gamora off the cliff to her death. As she died, the altar began to release energy, consuming Thanos as he tearfully shut his eyes. He eventually woke up, finding himself lying in a shallow pool at the base of the mountain, with the Soul Stone gleaming in his right hand.

Aftermath
"He mourns." "What does this monster have to mourn?" "Gamora. He took her to Vormir. He came back with the Soul Stone, and she didn't."

- Mantis, Drax the Destroyer and Nebula

Thanos, now equipped with four Infinity Stones, would leave for Titan to rendezvous with his children, where he would instead be ambushed by the Avengers, the Guardians of the Galaxy and Doctor Strange. The heroes were able to subdue Thanos, with Mantis using her powers to subdue him emotionally. The heroes were about to remove the Infinity Gauntlet until Star-Lord began to ask about Gamora. When Mantis stated that Thanos was mourning, something which shocked all of them, Nebula realized in horror that Thanos had murdered Gamora to obtain the Soul Stone. Furious at this revelation, Star-Lord lashed out at Thanos, which accidentally led to Thanos regaining consciousness and the failure of their plan, allowing the Titan to break free and overpower them, with the reminder of his sacrifice of Gamora serving to make him more determined than ever to complete his goal so as to not let it be in vain.

Eventually, Thanos was able to collect all six Infinity Stones. He snapped his fingers and wiped out half of the universe's population. Thanos found himself inside the world of the Soul Stone, where he met a reflection of a young Gamora, telling her he finally completed his mission. When she asked what it cost, he solemnly replied, "Everything", as he had lost the only thing he loved, his beloved daughter. Gamora sadly smiled before Thanos returned to reality.