[quote=@IncredibleBee]
<Snipped quote by Unoedipal>

Why does it not work as a personal skill? It's not like it's a legendary weapon or a blade beam.
[/quote]

Because it's the crystallization of his legend as someone who used improvised weapons, and we have an A++ Noble Phantasm in canon that does something of an incredibly comparable nature.

NPs aren't just magic items, they're crystallizations of feat.