Void Knight Recruitment

Try to join
Talk to the recruiter. He will tell you that you can only join if you prove your skill. He will ask for a torcher ring and a shifter ring.

Get the materials
Talk to the Void Knight sailor. He will take you to an island similar to the one in Pest Control. Find the single portal, and go into it. You will eventually see a torcher. Kill it and a torcher fire will appear where it died. Light a torch by using it on the fire. Next, find a shifter. Kill it, and a small portal will appear. Use a piece of papyrus on it, and get a shifting code.

Crafting the rings
Use the torcher torch on the ruby ring. Use the shifting code on the emerald ring. You know have the two rings.

Finishing the quest
Give the items to the recruiter. Quest complete.

Rewards

 * Void recruit helm, plate, and legs
 * Void ring