We meet the biggest mystery of Avatar: The Way of Water less than five minutes into the movie.

That mystery is Kiri (Sigourney Weaver), a young Na'vi child

the daughter of scientist Grace (also Weaver) from the first Avatar.

"But wait," you may ask. "Didn't Grace die in the first movie? 

I don't remember her having a child." 

You would be right on both co$unts! Grace did, in fact, die, 

However, she did leave behind her Na'vi avatar, which Jake Sully (Sam Worthington), 

Neytiri (Zoe Saldaña), and their scientist friends keep in stasis. 

That's a tulkun-sized underplaying of what appears to be Avatar's take on immaculate conception.