This book series is well basically one major crossover of multiple fandoms that I am a part of.
Astra Miststorm-Wayne is the daughter of Bruce Wayne (who we all know is batman from the dc universe, and if you didn't know then where have you been) and Hope Miststorm (Who is Radiant Hope from the mlp comics but humanized and alot different). Now how astra came to be is well.... basically king sombra followed hope to earth as to means to well you know. So he basically possessed Bruce Wayne when sombra saw that bruce was talking to hope and all. They did it but the thing is that astra has more of bruce then sombra cause Bruce's willpower is strong enough.
Now when hope found out she became pregnant, she went into hiding as she didn't want king sombra and his family or Bruce's enemies to find out about astra.