Chibi-usa had ran into crystal Tokyo looking for her mother Neo Queen Serenity because she felt something happened to her mother who was the Queen but also the future version of Sailor Moon and Chibi-usa transforms into Sailor Chibi-moon just incase something happened until.

“Small lady..”

It was her mothers voice and Sailor Chibi-moon followed it until she ended up into a Dark Kingdom where she sees Neo Queen Serenity except she looked evil and she holds her staff while sitting on a throne.