Oh, oops! This version only covers Act 1; each of the LIs has a couple of minor interactions and a major "side quest" in Act 1 before you get into Act 2 (where the routes branch off). You can hang out with both Liam/Faye for the minor interactions, but only Liam is available for the "major side quest" due to spoilers.
I'm sorry about that D: I'll add a little blurb to the description to make it more clear.
(And you're actually right, Sei is the closest to the "secret route!" I hope that people play his route last.)
EDIT: I've updated the page with a little guide, if you still need!