In the end, it really hadn't been that difficult to achieve world domination.
Rumours had spread about the 'failure' of the East Heavenly Kingdom to maintain their sacred duty and keep the [relic] safe and that had led to rival kingdoms sensing an opportunity, a possible weakness.
Princess Mint had been glad to show them otherwise and by the time the dust settled it was more of a North and East Heavenly Kingdom.
And when that fracas was over, neighbouring kingdoms began to petition to join the kingdom, wanting the protection of such a powerful ruler. She had dumped that job to Maya but it still meant the Kingdom grew rather rapidly. (Except the time when Corona had sent in its letter and Mint had personally given it special almost-my-capital status.)
Then came those with minor [relic]s of their own and she kicked their asses too. Because if she, Princess Mint and defeated Valen, the greatest of Aeons, and had once possessed the Dewprism, greatest of [relic]s, she would eat pumpkins again before she let those weak jokers beat her. Rue helped because he was interested in anything to do with a [relic] until Mint simply appointed him as the kingdom's official [relic] advisor. The two of them went on frequent expeditions to find another [relic], even after they managed to bring Claire back using [relic] fragments. After all, Mint still wanted a [relic] for world domination.
Eventually her father decided to retire from the throne and Mint became the Queen. Her first edict was to have pumpkins banned from her kingdom but the punishment was simply to clean out latrines so one simply had to decide how much they really loved pumpkins (and cleaning latrines). Next she had named Maya vice-Queen to do the boring stuff while she went out to find her [relic].
One year after her coronation, Wylaf had flown down from his mountain to keep his promise to serve her once she ruled the world. Mint was actually surprised because she still hadn't managed to keep a [relic] (finding was easy but they kept breaking or being owned by megalomaniacal beings that had to be put down which usually resulted in another broken [relic] and the cycle would repeat itself) but a check with the maps of the world showed that the East Heavenly Kingdom essentially ruled all of it. Having a dragon wasn't so bad though. All overt rebellions against the Queen stopped instantly and the remaining minor holdouts just gave up and submitted to the new world order.
Princess Mint (because she was always the princess for those closest to her) never did find her [relic]. But she did get to rule the world with her friends by her side. And that's what she had always wanted anyway.