Based on a post by tumblr users Nemesis-is-my-middle-name and Answrs.
"hear me out: postcanon p:la and due to Shenanigans, everyone EXCEPT ingo gets (temporarily) yeeted to the future"
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Sinnoh had made its point. For whatever reason, be it punishment or trial, there were no other humans to be found in Hisui.
He was trying to make peace with it.
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