Ys VIII scripts use RPN arithmetics to perform conditions and some arithmetic calculations.
There are many different types of operations managed by the game, 63 in total apprently, with codes going from 0x1 up to 0x45, stored as 16 bits integers.
Find bellow some of these operators codes.
The main function found by weaknespase is located at the address .text+0x0029E876 from the unpatched japanese vita eboot. It contains a simple switch on these opcodes.