Quest was fixed. Nas had to come in a reset an NPC that was directly affecting the Fenrir npc. Do what miku said try doing the questline here:
http://ffxiclopedia.wikia.com/wiki/Food_for_Thought and finish it to the last quest, but you don't have to complete the last quest. If you have done that, or the quest still isn't giving you fenrir, then you'll need to contact Nas like I did. Don't contact him until you have done the link above. In my specific situation, I couldn't do the quests above because one of the npc's wouldn't take food, then that npc affected fenrir npc so I couldn't finish the quests or get fenrir lol. This post is 2 years old, so I am not sure if it was ultimately fixed somehow by nas or if more people are affected. Just try to finish the quest line above.