Infiltrating the colony in a stolen Leo, Heero came across Wufei and his Gundam. Unfortunately for Heero, Wufei was working for the people who kidnapped Relena. Meanwhile, Trowa attacked Duo with a new Serpent mobile suit, being previously captured by Wufei. Heero fought his best against Wufei , but the decades-old Leo was unable to hold up to a modern Gundam, and the Leo was defeated.
Determined not to give up he presses a button in his sleeveless top speaking in the communicator. " Cerberus initiate "
Solid Wolf and his two brothers then raids the colony " our target is aiding Heero and Duo to rescue Relena limit casualty to civilians but do not hold back on the enemies " , while Heero demanded that Wufei self-detonate his Gundam, and at that time Trowa had launched two missiles in Duo's direction, which created a haze that covered the corridor Wufei and Heero were in, giving Heero the opportune moment to escape.
Heero , Duo and the members of Cerberus found that they were too late to save Relena, but learned that the coup was being carried out by their former boss Dekim Barton, who wanted to drop the colony on Earth as part of a renewed Operation Meteor. Rushing to prevent its fall, Trowa reveals that he was only pretending to support the plan, and the trio were able to stabilize the colony. After getting word from Quatre that the Gundams were safe, Heero requested that Quatre send Wing Zero to him and he devised an escape plan from the colony by pretending to be unconscious.
Taking a shuttle, he met with Wing Zero in space and hurried to Earth to save Relena. However, his path was once again blocked by Wufei, and a battle from space to Earth ensued. It was during the battle that it was finally revealed why Heero no longer had the will to fight anymore. Heero almost let Wufei win the battle against him unopposed. While they both fell to Earth, Heero asked Wufei a simple question, revealing that the little girl and the dog that Heero accidentally killed years ago was still haunting him. He apparently relived the moment over and over, asking Wufei how many more times he had to kill the girl and her dog, before it would all be over. Speechless, Wufei watched as Heero gave up the fight and allowed his Gundam to plummet into the ocean. Knocked unconscious in the fall, Heero was later woken up by Wing Zero, which told him that he still had a mission to accomplish. Heero reluctantly replied that this would be their final fight together.
Flying to Brussels, Heero used Wing Zero's buster rifle to heavily damage Dekim's shelter with precise accuracy. However, due to the damage the Gundam had received from its previous battle, Wing Zero could not sustain the continuous recoil of its own weapon, resulting in its destruction. Battered and exhausted, Heero entered the shattered base, only to collapse into Relena's arms shortly after vowing never to kill again. As the world moved towards peace and mobile suits were eliminated for good, Heero continued to watch over Relena acting as her bodyguard as he began living his life free from war and violence.