I was looking on Allkahazam and saw that people already got there friend! Heres the guide.

I hope this helps! This is the info I have compiled:

Part 1
Talk to Luto Mewlirah in Upper Jeuno just past the AH and the church.
She asks you to help her investigate people in Jeuno who carry mirrors.
This is where you choose your race/gender of your NPC friend.
When you go around Jeuno, certain NPCs like Red Ghost in port, and Akta in Ru'Lude Gardens will ask about the characters physical features. "Was her hair up in a bun? Was it this color? etc etc". This is the CHARACTER CREATION process cleverly disguised, because this will determine how the NPC will look.
When you've talked to at least one, talk to Bheem the NPC at the gate to Battalia Downs in Upper Jeuno for a cutscene. After that, go talk to Luto again for a Silver Ingot.

Part 2
Zone out of UJ and come back to Luto for another cutscene involving a little girl that's gone missing. Go talk to Bheem and he says your NPC friend went to Eldeime Necropolis after talking to that same little girl.
Go to G-8 entrance to Eldeime Necropolis in Batallia Downs
F-9 in Eldeime Necropolis is a ???, talk to it to trigger NM battle. You do the battle with your new NPC friend. It was REALLY easy since your NPC friend will help quite well.
After NM fight return to Upper Jeuno and talk to Luto for another cutscene. After the cutscene, zone out of Upper Jeuno and come back and talk to Luto again for another cutscene.

Part 3
You and your NPC friend are sent to Sandy to find another magic mirror.
Talk to Portaire in Cargo Room B of Port Sandy for a cutscene.
After that, head to Ghelbsa Outpost to the hut.
You'll get a BCNM fight called "Mirror, Mirror"
The fight is 1 on 1 capped at level 40 against a Carrion Dragon, and isn't too hard even if you stroll in without appropriate gear.
Halfway through the battle, your NPC friend will join you to help you finish things off. After the battle, head back to Jeuno and talk to Luto. After the cutscene you'll get the "Signal Pearl" and the ability to call on your NPC friend in future battles. Happy hunting!

Edit: As far as I know, you get no say in the job of your companion. Mine is the Mithra named Raka Mhaimov, she wields a sword and shield and has Provoke. I suspect she may be a Paladin or a Warrior, but I will have to conduct more testing to see.

Also: Didn't realize there was another compilation up when I wrote this, sorry...

Edit2: The AI so far is fairly intelligent, and managed to keep hate during the Dragon battle despite Ramuh whacking away with the best Bloodpacts I could dish out. At the very least, the AI knew to keep hate off of soft ol' me. ^_^

Edit 3: Big update! If you go to a Rendesvous Point you can call your NPC friend to chat. Just talking apparently brings up idle chat about past events. You can see their level and "fighting style" (Mine says "Shield") or you can ask them to tell you what they're doing, when their HP is low and when their MP is low. At the moment, I cannot determine if you can change their fighting style, but I imagine you can.