I think it is equipped under Traits (or ability) and while equipped it converts the stats.
I don't think it is an active ability.
(Speculation, I am not high enough level to get it yet, but you should get Heavy Slash 1st)
FFXIV: Karamethien Seraphus
Still a Seraph Samurai Wanna Be
Fishing AF - Complete, SAM AF - Complete, RNG Af - Complete, RDM AF - 1/6