Board Thread:Questions and Answers/@comment-32073823-20170605091742/@comment-31763506-20170609122534

Fluid-decanter wrote:

VisionController wrote: Another question about the investments. When certain investments must be done before the reunion, in order to be ready in time for the BoY, Those done during megails path count as well correct? Correct. Excepting Premium Steel, I believe. That has to be done before Chapter 1 ends.

Seriously, you'll want to look at the Investments wiki page and the detailed Battle of Yhilin page. That should explain all the variables and you can determine what your priorities should be. (Alternately, you can use the save game editor to give yourself all the ProN you can spend.)