Okay I'll bite and list a few that I have in mind...:
Azura x Laslow: Because Laslow's mom is apparently a good singer. <_<
Felicia x Kaze: Flora's twin and Saizo's twin. Both loyal to Lord Avatar, both join you regardless of which path you choose...yeah they have in common. o3o
Silas x Mozu: Idk.
Ryoma x Oboro: Not a fan of Takumi tbh...
Subaki x Hinoka: Because I refuse to fucking acknowledge that Selena is Caeldori's canon mom PERIOD!
Sakura x Saizo: So that Asugi would look like Gaius.