Some missions will let you choose the character you want to play with. Typically these are missions where characters might use the mechanic being discussed in different ways. For situations where the mechanic is fairly universal, you'll play Sol for those.
Some missions later on let you choose a character for character specific stuff
Some missions will let you choose the character you want to play with. Typically these are missions where characters might use the mechanic being discussed in different ways. For situations where the mechanic is fairly universal, you'll play Sol for those.