Aqua is a Premium Box Tsum. She is a limited event Tsum and is not available from purchasing Premium Boxes outside of the event. She was introduced during the Japan Event Stitch's Cousin Search (September 2018) and the International Event Stitch's Cousin Frenzy! (January 2019). On the Japanese version only, she is also a voice Tsum.
Aqua will create 2 types of Tsums for a short while. Her base time is 4 seconds. She will create a lot of Shadows and a few Aquas.
Clearing enough Shadow Tsum Tsums would create a chain of Aquas. Clearing an Aqua chain will clear a really large area of surrounding Tsums. Clearing enough Shadows will fill up the skill meter at the bottom. If you used her skill three times, she will activate a special skill that will clear all the remaining Shadows after her skill finishes using her key blade. Try to be as quick as possible when connecting the Shadow and Aqua tsum tsums, and try to connect as much Aqua tsum tsums as possible, since she clears a really large area of Tsum Tsums.