What is this, and how do I get one?

Well don't Ark rings come with a set effect making them some what better than your generic ring?

Ark Ring as in the 9th Anniversary Ring? I never really pay attention to names of items.

If that's what you're referring to....because you need something like 9 other pieces of equipment to obtain the full effects, which means if you have any other set you're pretty much not going to bother. I only got the ring because it had Potential and there's not many special rings released in JMS.