I'm pretty upset that this recording bugged out unexpectedly, and did not have any audio whatsoever, and even more unfortunate is that it happened for the final boss of the game :(
However, no point crying over spilled milk because there's ZERO ways to recover the missing audio. The best I can do is manually add the Soul of Cinder music back, and the music transition between phase 1 and 2 was done manually so hopefully you find it smooth.
Sound effects on the other hand would be impossible to add back, they are straight up lost, which kinda sucks, but the visuals are more important for hitless run anyway, so just enjoy the BGM I guess.
I'm not going to restart another save file just to fight him, it's too much trouble even if I use save editor. I would rather move on to new things instead of wasting time on the same boss.
Tech issues aside, this boss is alright as I am fighting him within recommended level range and he is weak to lightning.