Mercenaries
Personal trials
A personal trial is a test that a fully grown mercenary takes with two companions. The First Breakthrough opens once your best floor passes 150, and further trials open one at a time on floors 300, 450, 700 and 850. Recruited regular mercenaries can take them just like named heroes.
Open "Personal Trials" on the Adventure tab, choose the challenger and assign two companions. A lost trial causes no injury, death or spending and does not advance the week, so you can change the party and gear and try again.
The Oath of Fellowship
A mercenary who clears the floor 700 trial swears the Oath of Fellowship. From then on their will no longer drops at year end, so they never retire on their own, and aging no longer costs them stats. If they had a retirement promise, that promise ends and a gap between deployments can no longer make them leave.
The oath does not prevent death in battle. It also cannot stop them leaving at zero morale or being released by you, so keep an eye on morale and injuries after the oath as well. See Will and retirement
Steps and rewards
First Breakthrough, floor 150. The challenger must be fully grown. All three must survive, and the challenger’s damage and healing plus half the damage they absorbed must reach 28% of the party total. Passing gives them the breakthrough look and one point of will.
Floor 300. Win with the challenger alive to raise health, attack and defense. If a mercenary needs more growth first, the screen shows how many stats are left.
Floor 450. Win with all three alive to earn the SS+ Unique Breakthrough and raise the potential cap to 118.
Floor 700. Win with the challenger alive to swear the Oath of Fellowship.
Floor 850. Win within the time limit with all three alive to fulfill the oath and raise the potential cap to 125.
Injured mercenaries and those away on an expedition take their trial after they return.