A lot.
FE4: Cuan
FE5: Dagda and Tania
FE6: Marcus, Zealot, Cecilia, Sophia, Douglas, Niime, Yuno, Dayan, and Yodel
FE7: Wallace, Marcus, Guy, Isadora, Louise, Vaida, Renault, and Karla
FE8: Mostly secret characters on the Creature Campaign. They don't contribute anything at all; Caellach, Riev, Orson, Ismaire, Selena, Hayden, Valter, and Fado
FE9: Astrid, Makalov, and Lucia
FE10: Leonardo, Aran, Fiona, Makalov, Astrid, Bastian, Meg, Heather, and ESPECIALLY Oliver