Additional information about this topic courtesy of Serenes Forest.
Adjutants are back up units that you can partner up with your characters. Once you unlock this feature once you’ve reached Professor Level C. You can only assign one adjutant per character but eventually you’ll unlock 2 more adjutant slots (max of three) as your professor level reaches Level B and Level A. Setting an adjutant is also a great way to train a lower-level allied unit and increase their affinity towards you at the same time. If the host falls in battle, the adjutant will safely retreat.

Deployed adjutants have the following benefits and limitations:
* Only gain 50% EXP in battle (mitigate this by equipping the adjutant an Experience Gem or Knowledge Gem prior to battle)
* Gain 100% of Skill EXP (except Authority)
* Gain 100% of the class mastery exp
* Gain normal amount of Support points.
You can set a Mission Assistant student from another house as an adjutant. That way, you can build up their affinity towards you, making it easier to Recruit them as soon as you meet their basic requirements. However, limitations to Mission Assistants still apply even when you set them as adjutants.
Unlike the “pair up” system of the previous FE titles, you can’t swap the “host” and the adjutant in the middle of the battle. Adjutants don’t provide Stat boosts to their hosts but depending on the class, they can provide the following Support actions to their partners.
1. Follow-up: Occasionally adds a follow-up attack in combat
2. Guard: Defends against and reduces Damage from follow-up attacks.
3. heal: Occasionally heals the host unit at the start of the turn.
* Even if the host misses, there’s still a chance to trigger an adjutant follow-up
* Adjutant follow-up attacks can’t trigger during the enemy phase.
* The adjutant must be able to reach the enemy with the same Attack Range as the host.
* Adjutants don’t lose Weapon Durability when performing a follow-up attack
* Adjutant follow-up attacks can miss or trigger a crit
* Follow-up attack Damage is equal to 50% of what the adjutant can deal if he/she was fighting the enemy alone. This includes Bonus Damage from their weapon properties but does not include double-attacks or Ability effects.

Activation Rate
| Support Level | Trigger Chance |
| None | 10% |
| C | 20% |
| B | 30% |
| A | 40% |
| S | 50% |
| Note: According to Serene’s Forest, if the host and adjutant has a C+, B+, or A+ Support level, the activation rate will still be capped to 10%. This applies to Byleth’s hidden “+” Support Levels. |
* Brawler
* Grappler
* Armored Lord
* Emperor

Here are some of the important notes about this Support action:
* If the enemy’s follow-up attack is enough to KO the host, he/she will survive with 1 HP. (Applicable even if the host is already at 1 HP).
* When the enemy triggers consecutive attacks, this action will not trigger for the 2nd attack. However, there’s a chance to trigger this on the succeeding attacks.
| Support Level | Damage Reduction |
| None | 10% |
| C | 20% |
| B | 30% |
| A | 40% |
| S | 50% |
* Monk
* Priest
* Bishop

| Support Level | Number of times to be healed |
| None | 1 |
| C | 2 |
| B | 3 |
| A | 4 |
| S | 5 |