Zelda

Zelda will be unlocked in Age of Calamity after you complete the Chapter 1 mission, Road to the Ancient Lab.

Like Link, Zelda has a number of different unique actions that you can choose from which are dependent on which weapon she is using.

If Zelda is using the Sheikah Slate, then her unique action will allow you to activate any Sheikhah runes that she has placed around the battlefield.

To unlock Zelda's second unique ability you must first complete the Chapter 6 mission, Each Step Like Thunder.

During this mission, Zelda will gain a new weapon - the Bow of Light - and, with it, her second unique action, which allows Zelda to switch between her normal form and her luminescent one. When Zelda is in her luminescent form, her attacks will be stronger and any enemies within a ring of light will take increased damage from her Arrows of Light attack. The downside, however, is that the luminescent form will grain Zelda's special attack gauge.