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.
Webthis page contains known demonstrations of blood demon arts in the series.
Webi'm pretty sure akaza's compass needle and his ability to create shockwaves with his attacks are both considered part of his blood demon art.
Or maybe it's anything he.
Webone of akaza's most defining abilities is his compass needle.