I would actually not mind it if Lightning's demon blade was actually a hammer.
No matter the context, I would mind if someone called a hammer a blade. x)
You see, usually it's like this:
Blade:
Swords, Knives, Daggers, Sickles, Scythes, Axes, Shovels...
May have a blade:
Spears, Halberds, Shakujou...
No blade:
Hammers, Picks, Batons, Staves, Section staves, Maces, Flails, Shields, weighted Chains/Ropes...
Blades can be sharp or blunt, but what differentiates a blade from a hammer head for example is that a blade concentrates the impact on a single point or line while a hammer head diffuses it.
And why some spears-like weapons and all picks are considered to have a "head" and not a "blade"; I think it's because they only concentrates the impact on a single point. But weapons like foils for example also only concentrates the impact on a single point and people still say it has a blade. I don't know...
But what's certain is that hammers don't have a blade because they diffuses the impact.
