Key of Osanalan
From Halopedia, the Halo wiki
During their childhood, James and Ruwan Ackerson used the imaginary Key of Osanalan to rescue a "Princess" as part of their make-believe games.
During the Human-Covenant War, James Ackerson, now a colonel in the UNSC Army, was captured after the Battle of Mare Erythraeum. While he was being interrogated by the Jiralhanae Shipmaster Lepidus, he said that the Halos would not properly activate without the Key of Osanalan, causing the Covenant to go on a misleading search for the "Key". Ruwan, after realizing the importance of the Covenant's belief in the key, contacted the Covenant, saying that he would give them the Key when they met. Once they arrived, Ruwan then told them that he was the Key. Confused, the Covenant brought Ruwan to their ship, the CCS-class battlecruiser Harbinger of Piety. Unbeknownst to them, Ruwan had been implanted with Tykos 30, an organic tracking compound. Moments before Nassau Station used its Magnetic Accelerator Cannon to destroy the ship, Ruwan told the Minister of Inquisition to "kiss [his] ass".
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