To become a ninja, an avatar must be a novice at Job Level 10. The ninja guild is located in the city o Amatsu. To get to Amatsu, an NPC near the wall north of the merchant guild in Alberta will take you there for free.
Once you get to Amatsu, enter the Ninja Guild Building and search for a room hidden behind a wall at the back of the main room. Inside this room, you’ll find Guild Master Couger Kai, who will ask you to deliver a message to his enemy in Einbroch.
After talking to him, make your way to Einbroch Tower. The cheapest way to Einbroch is to go back to Alberta via the same boat that took you there. Then take the boat to Izlude for 500 zeny and board an airship to Juno for 1,200 zeny, In Juno, switch from international to domestic flight and then get off at Einbroch.
When you get to Einbroch, make your way to the top of the tower where you’ll find a young man. The young man will then ask you to bring five cyfar and one phracon. Once you turn over the items, he will reveal himself as Master Couger Kai’s enemy. He will then give you his reply missive and whisk you off to Amatsu.
Back in Amatsu, seek out Master Couger Kai with the same items you brought his enemy in your inventory. Voila! You’re now a ninja.
The Gunslinger Guild is in the city of Einbroch, under the very tower where Ninjas find their guildmaster’s hated foe. Once inside, talk to the job change NPC and fill out an application. This NPC will then ask you to go to Payon.
Once in Payon, move to the southeast and look for Fansole. This NPC will ask you to fetch random items, the difficulty of getting which will be based on your avatar’s base level. Aside from bringing Fansole these items, you will also need to give him milk.
When you finish Fansole’s quest, return to the Gunslinger Guild, talk to the guildmaster, then put on your spurs and ten-gallon hat.