Zagi is a member of the "Red eyes" as they are referred to early on, due to the mook charicter signiture red eyes, on but is later revealed to be a member of Lethiathans claw, one of the five master guilds of the Dhangrest Union.
Zagi personally is a violent sociopath who only seems to draw pleasure from fighting and killing strong opponents leading to his role as an antagonist targeting Yuri Lowel.
Zagi fights alone and employs a number of rapid attacks that can stun the party, during which he is hart to hit as he alternated between spinning attacks and jumping attacks for his "Artes". His normal attacks are attacks with his duel daggers that he can combo to an extent similar to Yuri's attacks.
Later battles add other features to him, one such battle gives him the ability to drain magic attacks. Another gives him the ability to poison party members, poisoning himself in the process.
Upon mistaking Yuri Lowell for Flynn in their first encounter at the start of the game, Zagi quickly becomes obsessed with Yuri's Strength and becomes a recurring villain up untill the final dungeon of the game.
This is theorised by the party as him seeing Yuri as his "equil" and wishing to fight him constantly, Yuri however sees Zagi as nothing more than a thorn in his side.