Class rank

[Brids17]

Is this purely for hiring a new character with slightly higher base stats or does it have any effect on the existing characters?

[ShinkuTear]

If the generic unit is also of the same type as the class, and started at a lower rank, it will promote to the higher rank right away. So a tier 1 Warrior will turn into tier 2 right away, with all the benefits of this, including boosted base stats and possibly more spells/skills to use.

A tier 1 Fire element Mage might only get Fire, but Tier 2 would also have Mega Fire, Tier 3 would have Giga Fire... along with any other spells that come with those tiers, and the boosted stats.

In all cases, ranking up a class *also* boosts the units base stats when they next reincarnate, and this is your key to massive power, as these boosts are all permanent and all add together. Mastering every class will produce base stats of over 1000 during Reincarnation.

[Z3n]

Early in the game, you can pass a bill to allow your characters to pick a subclass, which allows you to level up another class instead of their regular class (I repeat, INSTEAD OF). Not so great for generics since they automatically rank up with all the benefits of the rank when leveling up their own class as ShinkuTear said, but there is zero downside in picking a subclass for unique characters (Killia, Seraphina, etc.), and leveling a class by subclassing counts toward class unlocks.