•Miyu:
The managraphic artist, is acquirable in Chapter 2 of either character's story. You do not have to get this character during chapter 2 (I got her during chapter 5 on my first playthrough):
Visit the Managraphics Shop and buy a managraphic from Miyu, you have to more then what she asks to have her join you;
Pay an extra 10,000 for a managraphic.
Once you paid her leave the Shop and rest at the inn for a couple days
View the the following events 'Cooking with Mana' and then repeat the above twice more for the other 2 events: 'Budgeting Blues' and 'I'll go with you'
You may have to rest at the inn for a day or 2 between the shopping and the events.
•Recit:
This character's events start in Chapter 3 and is acquirable in chapter 4.
Chapter 3: Once you begin this chapter view the events and you should see Recit (the messy Orange hair guy) talk to Macaroon, then leave.
After that event, go to Yoma King Castle L3: Baptism Path, and kill the level boss.
Once you walk into the room after the level boss fight, you'll fight Recit (then he runs away, poor guy..)
Chapter 4: there are 3 events to view here (in this order): 'Peculiar Incident', 'Register Vendetta' and 'Keep the Receipt'.
During the last one, you fight Recit again, once you beat him he will join you.
•Mizuki:
This character shows up in Chapter 4, and you fight her. She will join you during Chapter 5.
You fight this character during Chapter 4 and again in Chapter 5
During Chapter 5 there will be 2 events you will need to see: 'Convenient Setup' and 'Mizuki's Mizugi'.
You fight Mizuki again during the second event and then she joins you after that.
•Suzaku:
This character is only available at the end of the second playthrough on true end requirements. Once you beat him in the second playthrough at the last chapter, he will join you before you enter the final dungeon of the true end.