Crescent Unit Circulus is an enemy from Crisis Core -Final Fantasy VII-.
This foe is amongst the strongest of the Crescent Unit enemies, as it has access to the Energy spell in addition to chaining attacks with Chain Thrust. It is highly advised to use powerful attacks such as Tri-Thundaga, Energy, or Flare to deal with him as quickly as possible. In groups, he should be left last as his attacks aren't super hard to dodge.
Circulus is Latin for "circle" or "ring."