You know what's a scary thought that could actually happen?

I don't think Intelligent Systems is stupid enough to refine the tome that's locked to one of the most powerful units in the game...

Wait, nevermind.

Nah.

Dire Thunder's refine will be a Slaying Effect, Atk+3, and Heavy Blade effect.

Yes, yes you have a point. but what about.
DEATHBLOW 3
FEIRCE STANCE 3
SLAYING EDGE EFFECT
AND finally but certainly not the least.
"IF enemy has bigger hands than unit then unit will do another 'Attack twice' right after first 'Attack twice'

Things like this are why wrazzle-dazzle staff units are, and will continue to be, completely busted. DC/Vantage/QR Sword Rein? Not a problem. Slaying Edge/Quickened Pulse DC Ayra? Chump change. Vantage Bonfire Ares waiting for you? No danger. They made pretty much the weakest class one of the best counters to all their powercreep and shenanigans they pull and it's hilarious.

Base effect after refine: Unit attacks twice (Even if foe initiates attack, unit still attacks twice)

Unique Refine: Death Blow 3

Potential Build:
DB Refined Dire Thunder
Flexible Assist
Moonbow/Luna
Close Counter
Vantage
Flexible C Skill
Fierce Stance Seal (When it becomes a thing)