Requirements:
15 service hours ( a must) 5 hours from 3 of the people your angel tutor assigned to you
A good level or a good party (about level 15 if soloing or a group of about 5 people with 2-3 priests)
food/healing potions
Talk to Micheal to start the quest
Kind of a walk through:
Alright, after you get those hours and form a party head over to East or West Playgrounds to go over to the training grounds to collect the Cores for your quest. after you head in start to kill the monsters one by one till you get a core (or continue killing till your whole party gets one) continue doing this all throughout the map (Press ALT+M) to see where else you can get the cores. After your done head over to where the goat demons are then continue walking ahead till you get to a overly large angel statue, click on the pot thing so summon the guardian (if he doesn't spawn or appear go to A2 of training grounds)
-[{Warning!}]-
The guardian angel hits about 200+ every time, sometimes also surrounding damage... so be careful.., he looks like the evil side of Sephiroth... don't want to get on his bad side.. or did you?
Soloing: Make sure you have a good enough level (plus weapons, armor, potions ect.) have at least about 70-80 small potions which cost like 40 each and some mana potions or food, continuously attack him with skills or just everything you got while keeping a very very close eye on your health. Your mostly going to heal the whole time and i find it better if you kept your cursor on the potion and right click it whenever you can while pressing the F1~F12 keys for your skill or spell, i solo'd the guardian and it wasn't much of a problem although i almost died.
Party: forming a party of about 2-3 priests in it is a good idea unless you would like to waste food and potions while they heal you also, make sure they continuously heal you or you heal them so they don't die from the angels 200 damage every time.
After you get his necklace head back over to Micheal to claim your reward, Here's a pic of it: