The amount of experience rewarded was about the same as his mission for fighting against the Tyrant. Completing all the objectives netted him more than twenty billion experience, and this was basically the standard when faced with a Beyond Grade A task.
With the addition of political assets, Han Xiao's actual experience almost doubled, and his savings rose quite a bit.
Other than that, he also received a Legendary Point and a Character Summon Card.
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Star Field Legendary Point (Shattered Star Ring): [Battle with the Dragon Emperor]—Your battle with the Dragon Emperor will be added to your battle records, and your reputation will be passed on.