I've been disassembling bits of the game for some time now. I looked into the exact odds of charm getting a drop item a couple days ago.
Weapons and techs share a list of possible effects for modifying their outcome. Dealing magic damage, inflicting statuses, and special damage numbers (1/2, HP to 1, etc) are all handled by these.
There were two unknown until I found the chance of charm item the other day.