That oakwood.jpg is associated with the Boken swords under _GREATSWORD & is linked to the Kensei character creation due to the starting weapon being the nodachi_00_start. My suspicion would be something to do with the mesh, but I can't verify. Not entirely sure why the jpeg would cause a problem since the mesh should be linked to the *.dds files, but this is the only thing I can think of.
One possible easy fix is to do what the attached image shows.
Also, there are several polearm models loaded into the mod already that can meet the expectations desired (and I'm not entirely sure we ever added them to loot tables). \MODELS\WEAPONS\POLEARMS & \MODELS\WEAPONS\_POLEARMS
I'll start adding great hammers to all monk skills as well. @Phanjam I think I pretty much cleared out that to-do list tonight. No need to worry.
Check attached MONK.rar for all replacement monk skills. They now have updated requirement descriptions & addition of 2HMACE.
Check attached KENSI.rar for all replacement Kensei skills. They now have updated requirement descriptions, replaced all instances of "Sword" with "Blade" & addition of Polearms.
Check attached KENSEI_PLAYER.rar for replacement Kensei units for updated class description; however, I did not change the starting weapons.
This takes care of WM_1, K_1, K_3, K_4, & K_5 if my attached image instructions correct the crashing bug.
Need further information on R_1. Vicious slash looks fine for me within GUTS. I'll have to download the game overnight and I'll verify in-game tomorrow whether I can duplicate this error.