He will ask you for weapons, ten obsidian swords.
Most violent way to get them, kill guards at Tichticatl.
Easiest way to get them, steal from the Tichticatl armory.
Most honorable way to get them, buy from Atlipacta at Tichticatl.
To get the needed emeralds, sell parrot feathers to Paxaptamac.
Another way to get emeralds is to help the Jukari.