Fixten
Kai can still be alive if he use the same decibels sound to protect his ears when he use that super attack.. Same decibels power that collide with each other will neutralize each other.. Ears 100dc>collide area< superattack 100dc... That collide area will become neutral and will not effect himself... Thus protecting him and kill surrounding enemy...
With those sound waves(pressure waves) their entire bodies would start to be torn apart due to the pressure waves. The headphones wouldn’t have saved anything, and neither would his barriers he placed on his ears. Considering magic, Ayaka would have been okay with in the barrier, but not because of the headphones.