Alright, but I wanna give you a run down. Basically the protagonist had died along with his sister, and both are brought to the new world. After countless years spent bonding as an actual family and being trained in battle for the whole (new) lives, she dies; and that's how the new ark starts.
It drives the plot. It's like that one show where the first 3 episodes were nothing but thoughts on the main characters head. None of those events occurred yet it was able to drive the plot in it's first reveal!
OwO) / Welcome!