Daphtus: Draggon Boy (Book 2)

After the Legion and the Mark fought at Monera Academy, the Daphtians and the monsters learned to live in peace, even though the Mark hasn't been fully defeated yet. Torn Mark swore revenge on the Legion and promised his return.
Back at Monera Academy, a new boy, Heroid Troy, enrolled for the rest of the year. Even though he just came, Heroid showed amazing talent in his classes which impressed Hana, but worried Arthur. He suspects Heroid's true hierarchy because of his complete mastery over fire. Even becoming fireproof simultaneously.
But Heroid seemed like the least of their worries for the time being. Ms. Renn, the Weaponry teacher, disappeared without a trace. Without the best combat artist of Monera Academy, Monera Academy and the Legion's defenses decreased drastically. And Torn Mark can strike at any time which worried everyone.
Everyone except for Arthur.