Cnet's translation of the chapter:
http://mangahelpers.com/t/cnet128/releases/27630
Chapter 613:"The Mermaid Princess in Koukaku Tower" Discussion
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Pretty sure it was said or at least clearly implied that Vivi's mother had died some amount of years prior to the main storyline. agree that it doesn't have to be a very big deal, Vivi's mother certainly wasn't, but there's potential for there to be something to it so it's a solid observation regardless.
Not seeing it whatsoever.