How to unlock the Night Warrior EyesStart off by logging in to a level 110 character, and head for Bolarus. There you will be approached by Tyrande's owl Dori'thur with a quest. Accept this, then head to Stormwind to talk with Maiev Shadowsong. This will lead to you taking the portal to Darkshore where you will have to complete a few quest, following by a short single-player scenario that tells the story of how Tyrande became the Night Warrior.
The quest chain itself is not that long, and takes about 30 minutes to finish. Once you complete the scenario, you will get the achievement "In Teldrassil's Shadow", which unlocks the Night Warrior Customization option for all the Night Elf characters on your account.