Go to Sauromugue Champaign (L-10) (must go up the cliff at (L-8) first), 3 Sabertooth Tigers wait outside the cave. You can ride a chocobo into the cave to avoid them, but bring along an Instant Warp Scroll if you do not want to fight them on the way out.
In the cave, find and touch the the bones to spawn Old Sabertooth.
Wait for the Old Sabertooth to die naturally (~5 minutes). He will not aggro you if you stay at the back of the cave, even with the battle music activated. If you accidentally kill him, wait five minutes, then re-examine and he will pop again.
Examine the bones and bring the Old Tiger's Fang back to Perih to complete the quest.
If someone else started the process prior to you, actually seeing the old Sabertooth die (see the death notification text) enables you to get the key item without first examining the bones to spawn the Sabertooth.
Return to Perih Vashai and quest will be complete.
Note: If you do this quest with several of your characters, make sure you aren't holding the Ranger's Necklace from another character, as this will prevent you from completing the quest. If you do, you will get a message that you should return after sorting your inventory (normally refers to a full inventory).
In order to become a truly great hunter, one must be accepted by Mother Nature. In order for that to happen, one must gain the fang of a tiger, the fanged king. But it does not sound like any old fang will do...
SPOILER WARNING: Details about a quest, mission or other Final Fantasy XI in-game storyline follow.
Perih Vashai: Have you, my child, trod on many a land, drank from many a rrrainfall, fought many a fine battle and lived to see many a dawn?
Perih Vashai: Then truly I say unto you, unless you are apprrroved by the earth and the sky, how is it that you can say you are accepted by Mother Nature?
Perih Vashai: If you so desire to submit yourself to the laws of naturrre, my child, then go, meet with the fanged king of the beasts, and bring back one of his grrreat teeth.
Perih Vashai: Listen to the voice of nature and wait for nature to run herrr course. If nature accepts us, then even we who lack fangs will be perrrmitted to hunt as her rangers.
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Perih Vashai: For the hunterrr, the fangs are not just a tool vital for existence, but also a witness to its death. If the fanged one loses its fangs, it can no longerrr live. Yet when the fanged one dies, only its fangs rrremain.
Perih Vashai: To hunt like the fanged one, you must live by the fang and die leaving only the fang behind.
Perih Vashai: Onto you, our new ranger, I bestow the witness of the life and death of the grrreat fanged one...
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