Retainers, confirmed, you have to pay for them.

[Samburi]

They are going to make it so you want to pay for them. A majority of players will feel like they need it. That's how F2P games work with their cash shops. They create this "I need this in order to not feel like I'm missing a benefit of the game" This is pretty much a bump in monthly sub price for most and the ones that don't do it will feel like they aren't getting the full benefits of the game.

second character in the same FC + FC storage = no need to buy extra retainer if you don't want it.
And if you pay 6 months in a row the standard account don't cost more than the basic account.