Hey, there.
I've started the process of implementing Gen II support in PKHeX, following my just adding Gen I support.
I'm currently working on implementing save file loading/reading for GSC saves -- this is easy for English games, because bulbapedia documents save offsets well for those here.
However, Japanese offsets are not so well-documented; I'd like to ask, then, if people could help out by documenting them while I work on implementing the other features required for PKHeX's Gen II suppo