-This game would typically be on iOS/Android for use of the touchscreen.
The world is a swath with an over-saturated amount of magicians, at least half the total population. These magicians wield powerful magic cast by playing music. Because of this they are adored by the 'non-magic' folk, not unlike rock stars. This leads them to having a superiority complex or inflated ego. In some cases it gets so bad it drives some of these mages mad, losing their state of self and causing them to attack anything in sight.
You are a swordsman, who fights against the 'oppression' of the mages who go off the rails. Swordsman are very rarely seen anymore thanks to the overwhelming power that mage's possess, making it a very unpopular profession, regardless of known occurrences of them going crazy. You go through the game battling these lunatic mages and return peace to all parties involved.
The game works very much like an action RPG that relies on rhythm elements. You start on one side of the screen, the mage on the other. As the mage plays music to cast his spells they emit musical notes that require certain attacks from the player in order to destroy them, thereby deflecting or cutting through their spell. These attacks each have a sword 'type' for each magic 'type' and are activated upon certain actions on the touchscreen. To win a match you must destroy the mage's spells and attack them to whittle down their magic shield. Once their magic shield is down the next hit ensures victory. However, they also unleash their greatest 'rhythm magic' once their shield is down.
As you play and defeat mages, you earn currency and experience that you'll use for purchasing both new equipment and skills. Later in the game the mages will have an increased amount of magic types that they can cast, so buying new skills that match that type will be of the utmost.
-Game play Genre would be an Action RPG and Rhythm
-Target audience/rating would be for all
-Reference image from DA by, Knighteynight