>>30545355>>30545438>>30545489He was actually the last descendant of Alolan royalty, but it turned out he was infertile. This hurt his heart to the point where he pursued any means to recreate the legacy of his family.
He passed on his royal bracelet to his mimikyu and helped it make an incredible costume in a vain effort to perpetuate his family line. The mimikyu's fairy aspect gave it a great desire to help this human out with its goal. Acerola's goal in life now is to fulfill her master's dream, and it acts autonomously around Alola with its ability to mimick other creatures--in this case, a human girl.