Theory about Big Mom's weapon Napoleon

(English is not my first language)

Recently Imu had his (aparent) true face revealed.

He's also been shown using a Naginata-like weapon, the Naginata also has a black flame in it that can turn into other weapons, like a cannon or a wrecking ball.

This reminded me of Big Mom's signature homie weapon, Napoleon, which poses a similar shapeshifting capability, but Napoleon is seemingly limited to turning into different types of blades instead of just any weapon like Imu's Naginata.

Imu's naginata is being theorized to be a legendary weapon linked to Whitebeard's naginata and im basing myself of this.

What if, when she was younger, Big Mom saw or heard about a legendary weapon, or someone wielding it, that could shapeshift into other weapons, she found this interesting and based herself of this legend to create Napoleon.