Unlock Chapter 12 Gaiden
Complete Chapter 12 in 20 turns.
Unlock Chapter 21 Gaiden
Complete Chapter 21 in 30 turns. You must bring Fa and keep her alive, talk to Gale(Blue haired dragon master the appears in mountains) with Zeis & Milady.
Unlock Chapter 16 Gaiden
Complete Chapter 16 and keep Douglas Alive (The General with a portrait.