Here you can find 2 scriptlets that will let you either change the ME that should be played right after winning the battle or play a short SE for every actor that did level up then.
Both have something in common: the LVL_UP_SOMETHING_SETUP constant where SOMETHING stands for either ME or SE.
It is an array that needs 3 values: the "Filename", the Volume, and the Pitch.
The rest of the process is taken care of by the scripts themselves. Now just win the battle and you'll be listening to them in no time.
The Level Up ME Script
Ruby:
# * Level Up ME ACE * #
# 2024-01-23
class << BattleManager
LVL_UP_ME_SETUP = ["Victory2", 80, 100]
LVL_UP_ME = RPG::ME.new(*LVL_UP_ME_SETUP)
alias :kyon_lvl_up_me_play_btl_proc_vict :process_victory