While Conqueror’s Haki is only available to the few individuals born with it, Armament Haki and Observation ... During the Levely, Sabo infiltrated the Pangaea Castle and spied on Nefertari ...

At the same time, Sanji also possessed his finely honed Armament Haki, which is clearly strong enough to sustain the flames ...

Since Franky hasn't had a power-up in a long time, Armament Haki would be a great upgrade for the One Piece character.

Poseidon connects to Conqueror's Haki due to its ability to control the Sea Kings by exerting their will externally. Pluton correlates to Armament Haki based on its devastating firepower.