Arena Circus is set in a fantasy universe where physically superior beings known as 'Reavers' rule over high society and have established a strict caste system with humans at the bottom. In order to have any sort of nice lifestyle the humans seek out strong Reavers and allow themselves to be bonded as a 'Harlequin'. Some humans then are used as servants, jesters, pleasure slaves, etc, but most are forced to duel in arena-styled tournaments.
To the Reavers, fighting is thought of as an activity for the lesser beings, so disputes are handled through political power moves. But they're not above a little violence. Duelists known as 'Ringmasters' use the humans in battle by channeling their energy through use of a special collar the bonded humans are forced to wear. These collars, known as Rings, were invented by the royal families' ancestors a century ago, and are distributed through the government to any Reavers that decide to take a Harlequin. The collars allow the humans temporary use of their power, and any damage taken is transferred to the Reaver's more durable bodies through the technology in the collar, so that humans are able to battle over and over again with limited damage.
The two protagonists are Aldrich and Lilié (the player will be able to give them their own names depending on who they choose). The two are trying to battle their way to the top of a world that looks down on them, and soon it becomes far more than just a matter of pride.