Webapplied fighting spirit sensing is a bda for akaza.
He has a blood demon art, compass needle, which applies it to combat, therefore making it a bda since it's an unnatural ability.
Webakaza's blood demon art, destructive death, merges shockwaves with martial arts, making him a deadly combatant.
Akaza's compass needle technique grants him awareness of opponents'.
Webboth are his blood demon techniques called hakai satsu or destructive death, though yes the compass needle is the secret behind akaza, and it the most powerful defense weapon he has.
You can know how it works from the manga.
Webthis page contains known demonstrations of blood demon arts in the series.
Webjust simply roll a blood demon art in the old man, he has a chance to give you it depending if your lucky or not.