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When Osiris arrived in The Last City after the remnants of the Red Legion captured his Sundial on Mercury and utilized it to break time in a bid to undo their defeat in the Red War, Harper joined Ikora Rey and Aunor Mahal in a meditation chamber to interrogate the former Vanguard Commander about his reckless actions in creating such a dangerous device. Harper noted that his order were unsure if it was the real Osiris before them or a escaped Vex simulation or one of his Echoes. Osiris attempted to defend his actions by revealing it had been a bid to go back in time and save Saint-14 from dying in the Infinite Forest, but Harper angrily noted that he was far too calm for someone who had potentially doomed them all. Osiris shot back that if death was so frightening to Harper that he should rethink being a Thanatonaut and argued that humanity was in desperate need of more aid and that far more dangerous men then him were roaming free. Before Harper could question Osiris again, Ikora asked him and Aunor to leave the chamber. Although irritated by the dismissal, Harper complied with the Warlock Vanguard's order and left the former mentor and student alone.
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