As a way to try out units you haven’t unlocked, or to bulk out your army for a short period of time, we have introduced a system where you can recruit units to fight by your side for up to seven days.
We first introduced mercenary units in September 2019, which were distinct from regular troops on the unit tree and were permanently bound to your character. Similarly acquired via the War Scholar screen, Auxiliary Units are instead comprised of the same standard units that you can currently unlock with Honour, only they will fight for you for free. These week-long warriors come equipped as per standard and will earn Unit XP and Veterency Points for the duration of their service, but will only fight for you for until Monday before they vanish from your Barracks. Note that when you later unlock the unit with Honour, the Auxiliary - along with its saved Unit XP and Veterancy - will become permanently available.
Don’t expect to be able to fill your ranks with Iron Reapers. There is a limit to how many mercenary units you can recruit and the type of units available will change periodically. Just bring up the War Scholar screen (press X), then select ‘Auxiliary Units’ from among the left-side icons to see what’s currently available.