This quest can be completed as many times as you want!

Go speak at night to Dionysus Argantma (1015,1010,0), the priest centaur, located in the city of the Centaurs and say to him lute of peace. By following the conversation, he will give you his Peace Lute, which you will need to recharge.

Find 6, 8, 10, 12, or 14 Magic Lutes dropped by Silversky's Morbid Goblin.

Use the Ethereal Key, obtained through the Aetheric Isles Access Quest, to go to the Ethereal Isles. You must bring your Magic Lutes to Glaenshenmilandira (1970,2810,0), located in the center of the Ethereal Islands, which will be in charge of recharging the Lute of Peace via the keyword Lute of Peace.

Finally, bring the recharged Peace Lute to Dionysus Argantma, the centaur priest, located in the city of the Centaurs. He will give you your reward using the keyword Peace Lute (for this step you must talk to him at night).

Reward: 1 Celestial Robe (non-systematic gain)