Who is Strelitzia in Kingdom Hearts 4?

gamesradar.com:

Ever since the reveal trailer for Kingdom Hearts 4 dropped, fans both old and new have been asking who is Strelitzia, the orange-haired girl in the white dress that appeared in the trailer?

Unfortunately, as should be expected with the Kingdom Hearts series, there isn’t a straightforward answer. If you’ve played the mobile game, Kingdom Hearts: Union X, however, Strelitzia (pronounced like "struh-lit-see-uh") should be a household name to you. 

Spoiler warning: The rest of this story will delve into the events of the Dark Seeker Saga in the Kingdom Hearts series, meaning if you haven’t played all of the games yet but still want to, we suggest you come back and read this later. 

To understand who Strelitzia is, you first have to understand the mobile game Kingdom Hearts Union X (also known as Kingdom Hearts X, Kingdom Hearts Unchained X or Kingdom Hearts: Dark Road - just to make everything even more confusing.) In Union X players are sent to Daybreak Town - which is set prior to the events of the mainline series (Sora, Donald, and Goofy’s story) - and find out the series' main antagonist Xehanort’s origin story and how he turned to darkness. 

To put it as plainly as possible, Strelitzia is a keyblade wielder from this time and her story takes place years before Sora picks up a keyblade and teams up with Donald and Goofy. As mentioned above, Strelitzia was introduced in Kingdom Hearts: Union X and unfortunately - spoiler warning - also meets her end during the mobile game too. Which is why it’s such a surprise that she’s popped up in the Kingdom Hearts 4 trailer, considering she and Sora haven’t crossed paths much before and she is supposedly dead. 

Nothing should come as a surprise to Kingdom Hearts fans anymore though,