Hey, Pating, I'm not sure I can help, but we can give it a shot. I've been doing a bit of element tweaking for my own CC project.
Looking at my notes. The seventh byte of an element stat is used to determine the grid level (cost). Vital Force is set to '0' in the US version, which is correct
139 VitalForce
00 01 02 00 00 80 08 00 1D 50 00 00 00 0F 00 02 00
01 B3 00 00 00 05 10 FF FF 00 00 00 00 00 00 00 00
02 00 00 00 00 00 00 00 00 00 00 00 00
I'm on mobile at the moment so I don't have the ability to find the bin address for that block, but it's probably in a different location on the Japanese version anyway. That's what I'd look at first, and barring that it's probably something in the actual battle engine logic or the EINS files (which aren't well understood). Hope that helps.
Edit: One other thing I thought of. Since the elements used for VitalForce aren't the same level, this probably is a bug related to how game executes dual techs. I'd also check other unequal techs to see if they have the same issues. I think SwordStorm and DragonSpike use different levels.