Gyakusou runs small to ridiculously small, you can't even consider regular nike sizing because it's so fucked. You have to think normal sizing and size up one and even then the jackets may be too small.
Jackets have been, in my experience, pretty much a size up one ordeal. The shirts, however, are bat-shit crazy. I own one of the dri-fit tees - I'm on the small side of larges in normal nike stuff. Got an XXL, and it's quite close to not fitting - probably could have used XXXL.
Last season's jackets seemed two sizes too small so I passed (my xl fits perfect). I never copped any tees because I don't think they're that great and kunk said they fit like straight jackets on him. Since I mainly just sprint and run to the gym I don't need anything super warm because I get hot easily so a light jacket is all I need.
Last year they had some without hoods but it doesn't appear they're doing any like that with just a higher collar.