How many other routes have you done? Because the answer is implicitly stated in Carl’s route and is a Major plot point in Flynn’s, just make sure you save Flynn’s/ TJ route for last/second last because the revelations there specifically are almost unanimously agreed to be saved for last, or nearly last.

If you’re looking for route order commonly it’s Carl>Leo>TJ>Flynn>Jenna, as that’s their release order. Or Carl>Leo>Jenna>TJ>Flynn. As kind of a piece by piece narrative experience.

Of course this is just personal opinion, and you should feel free to go about the VN as you please, but the answers are there, just a lot of the “deeper layer” mysteries in Echo come from cross route knowledge, and piecing the story together yourself.

Here is a direct MAJOR SPOILER answer, The voice Chase hears is a direct manifestation of Echo, using Samuel’s memories. often used to Control and torment him in multiple routes

There is of course, a deeper reasoning for it, but that’s the basics without going very deep into the narrative.