Rise of the Third Power

To unlock the final crafting book for everyone's ultimate you must:

Rowan: Complete the Side Quest "Port Manteau" in Chapter 5

Corrina: Complete the Port Hole Arena (Hypothetically possible before in Chapter 5 Udingrad, but best done in chapter 6 immediately after regaining navigation

Arielle: Complete the Side Quest "Liberate Telindra" in Chapter 7

Reyna: "Bless the Rains down in Ardo Rita"

Aden: Complete the Side Quest "Aden's Childhood" in Chapter 5

Rashim: Complete the Side Quest "War Hero" in Chapter 5

Natasha: Complete the Side Quest "The Rezhov's" in Chapter 5

Gage: Beat the boss of Thunder Isle during the "Bless the Rains down in Ardo Rita" Side Quest in Chapter 6.

Here is a list of sidequests with location screenshots: https://gamefaqs.gamespot.com/ps4/350966-rise-of-the-third-p...