Below is a list of some characters in the game and how to recruit them to your team.

Stefan - Recruit Stefan in the desert level where you figut Muarim and the Freedom Fighters. Send Mordecal or Lethe to the upper corner of the desert, where there is a Bird Tribe member. Have one of them stand on the square there, and eventually Stefan will appear.

Sothe - To recruit Sothe, head to Chapter 12. He can be recruited there via the Info Menu.

Calil - Calil, too, can be recruited via the Info Menu, but in Chapter 20 instead of Chapter 12 like Sothe.

Largo - Like Calil and Sothe, Largo is also recruited via the Info Menu. To do so, consult the menu during Chapter 25.

Shinon - Shinon can be recruited if you have Rolf talk to him (since he will not attack Rolf like he will everyone else). Ike will then fight Shinon, and must win, in order for him to join the party.