Update on this for anyone searching google, I've made significant progress in cracking this and am working on a tool to easily edit the game text. I won't post any further updates on here since it's a bit out of scope for the forum, but do get in touch if you're interested in this sort of thing.

Hi all, I've been recently researching the game Suzumiya Haruhi no Heiretsu, a 2009 Wii 3D adventure visual novel game by SEGA/Kadokawa/AQ Interactive. Without going into too many details, It's an interesting game in a few ways, notably that the plot was written by the author of the original novel s...