That has got to be the decision to have Zack tag along in the adventure during Chapter 02.
Not only did that choice improve Chapter 02, but the entire story. It was such a dramatic shift in my original plan, that I ended up rewriting most of the overarching plot and shifted to a more personal-character driven story.
Now it did end up making the flow from Chapter 01 to Chapter 02 feel a bit slow, and there's this awkward sense that the story just doesn't wanna start. Because I kinda had to manouvre my way out of certain setups and weave a different thread, while keeping in line with was already established.
The result will be a far stronger and cohesive story in Chapters 3, 4 and 5.
EDIT to add: That the changes I made, and the rewrite I did, were in service of themes and plotpoints I was already working with. But it expressed them in a better and more dramitic way. I just decided to take a different road to get there.