Lavitz Slambert is a captain of The First Knighthood of Basil, a military unit of the kingdom of Basil. He is a loyal follower of their ruler, King Albert. Lavitz follows in his late father's footsteps, joining the military and siding with Albert.
Lavitz is a loyal, kind, and selfless man. He makes many sacrifices in his life for others, caring not for himself. He is also a powerful warrior, using spears and lances with extreme skill. His additions are generally slower than Albert's (who uses the same additions/weapons when replacing Lavitz).
When Dart first meets Lavitz, it's in Hellena Prison. He helps Dart save Shana, and the 3 escape to their kingdom. Not too long after, they meet Greham, the bearer of the Jade Dragoon spirit. He had killed Lavitz's father, and Lavitz sought his revenge. Upon defeat, Lavitz was chosen as the next holder of the Jade Dragoon spirit, not knowing it would lead to his death.
King Albert is kidnapped, and held at Hellena Prison. Lavitz's loyalty is never-ending, leading them on a mission to save their king. It is there that they take down the warden, Frugal. Then, as Lloyd was extracting a mysterious Moon Object from the king, Lavitz transformed into a Dragoon and attacked. However, Lloyd wielded a sword called the Dragon Buster, which is a guaranteed kill on dragons or dragoons. Lavitz perishes, leaving the Jade Dragoon spirit to Albert, who decided to avenge him and replaces him in the party.
Lavitz later appears as a ghost of sorts, being possessed by a demon. He regains some control long enough for him to kill himself (and the demon inside him) and help the party get past.