To help a Minion grow, you need another Minion.

Since a Minion's body is made up of pure Aether, you have to increase the Aether concentration for them to grow.

Once a Minion has grown strong enough, you can use Minium to evolve it.

Minium refines the Aether inside a Minion and leaves a branding in the form of wings behind.

Depending on the number of brandings, you will feel how your Minion gets stronger.

But make sure to remember that special-type Minions cannot be grown or evolved.