Adalbert loved his fiancé, Julia dearly, and was willing to turn on those he called friends to avenge her death. And while he seems to have good intentions, he is ruthless.
Adalbert is the first important character that Yuuri meets in Shin Makoku. He is Julia's former fiancée and abandons Shin Makoku, as he feels that the way of the Mazoku is wrong. He believes that the Mazoku are simply pawns of Shinou.
When Yuuri first appears in their world, Adalbert saves him from the villagers throwing rocks at him. Conrad shows up, riding a horse, and fights him, while Yuuri is carried off by a kotsuhizoku. Adalbert retreats, but not before telling Yuuri he would come back to save him.
Keeping his word, Adalbert shows up to persuade Yuuri to join him. However when Yuuri refuses, Adalbert tries to attack instead. Gwendal shows up just in time, saving Yuuri, and scaring Adalbert away.