The Wyvernite Armor is unlockable by collecting the Armor Fragments hidden throughout the game. The Armor is needed to beat the Finale chapter and reach the final boss. Each world contains 1 Armor Fragment, which can be missed due to branching paths.

Armor	How to unlock
Wyvernite Armor Fragment 1	World 1 Stage 5, take the upper path by jumping with the Hawk knight.
Wyvernite Armor Fragment 2	World 2 Stage 3, after going uphill, take the upper path by jumping with the Hawk knight, then jump again at the end of the platform.
Wyvernite Armor Fragment 3	World 3 Stage 1, when the sign comes up for the Hawk Knight to jump, this time, DON'T jump. You'll land on a lower platform.
Wyvernite Armor Fragment 4	World 4, Stage 4, take the highest path by using the Oceaneer at every water geyser.
Wyvernite Armor Fragment 5	World 5, Stage 9, after leaving the top tower and flying with the Griffacores , you'll catch a glimpse of the armor below. Drop down low to grab it.