Coox's massive works on Nomonhan (combined or in two volumes) and Changkufeng still offer up the most detailed coverage of IJA units in combat that I've seen. Drea's paper on Nomonhan is great and freely available here. apps.dtic.mil/sti/citation...

I won't get bogged down in recommending various Asia-Pacific War campaign histories that by necessity have to mention the IJA, but here are some standouts that either draw upon Japanese sourcing or have otherwise decent coverage of the IJA.