Well, I was on my Paladin so...
Ignoring that I would never let Nanamo drink the wine in the first place (I found the vial after all and KNEW someone was getting poisoned in advance)...

First I'd have encouraged everyone to make a stand against the Brass Blades and the corrupt Crystal Braves. Individually they're doomed, but as a team we'd make a force to be reckoned with. I'd tank, being the warrior of light, and cut down every last one of the traitors with Y'shtola healing me and the others providing much needed damage. I'd advance with the Scions to face off against Ilberd and bring an end to his life along with the evil Lolorito.

My need for blood will not be sated until every one of those traitors lies dead and their ashes scattered to the four corners of Eorzea. No one kills Nanamo and lives.