Amun does not follow normal hate patterns. With any other Abyssea NM, the first person to take action against the NM, through melee, magic, or job ability, that person would be the one who gains the Key Item.

However with Amun, one must make 2-3 actions to ensure positive hate. This is also an issue with actually claiming. Several times in the past few days, my linkshell has attempted to claim, and after using Provoke, Stun and Chi Blast, the NM starts moving towards that person, and almost immediately returns to an unclaimed status, allowing other groups to claim.