So, I spent a long time contemplating my idea, and it does kind of require multiple different features.tools to be implemented for it to work - however I think the idea is solid.

Tool 1: "Entourage", Companions, Escort, Garrison
Allows you to select up to 6 Sylesti (order does not matter) and add them to your Entourage. This feature is similar to Party, but also different.
The following limitations maybe? applied while assigned to the Entourage:
*Mutually exclusive with Party (Sylesti cannot be in both)
*Cannot be sold, traded, etc.
*Total slots could be increased via purchase.
*Cannot do things that would affect Sylesti Stats, as necessary by programming, or snapshotting
**Equipment Adjustments
**Proficiency Points
**Expertise Levels (Preferably could gain points but not the actual level, maybe have daily update)
**Experience Levels

This part might be where people start to lose me, hopefully my example is sufficient even if oddly timed

Tool 2: Multi-Stage Encounters
Upon starting a Multi-Stage Encounter (trademark pending), you are given a choice of which Sylesti to use, from amongst your Entourage. Assigning them to the different stages of the encounter based on the slots provided. Players could possibly get some small information based on the encounters ahead in order to make dynamic choices.
For example, I will describe a 1/3 encounter. In this, you assign a single Sylesti to be in stage 1, and 3 Sylesti to be in stage 2. Once you begin the stages, during stage 1 your "party" of available Sylesti will automatically be the Sylesti assigned previously. During stage 1, your lone Sylesti will attempt to do as much effort as possible before ultimately (inevitably and intentionally) "failing". The goal is not to "win", but to be effective. Then, afterward, Stage 2 begins, and the party will be the 3 assigned Sylesti from earlier, and they must try to win the encounter with having help created from the stage 1 effects. These effects potentially would include things like:
*Damage dealt to the enemy would be stored as a debuff on the enemy, increasing damage taken by the enemy until the stacked damage effect is overcome
*healing/absorb dealt to stage 1 party might also return as healing/absorb per turn over the course of say 10 turns split among the party
*effects on a per element basis could also be applied in addition or in replacement of the generic damage/healing, such as:
**Water: Absorbs 40% of the damage and healing dealt by the foes during stage 2, until the absorb effect is overcome
**Shadow: Damaging the enemy has 40% life stolen until the effect is overcome
**Fire: When damage is dealt to this target, 100% of it is duplicated and split among all present enemies
**Air/Wind: Periodic Damage Dealt is increased by 300% until the effect is overcome
**Earth: Damage dealt by the enemies is decreased by 75% until the effect is overcome
**Light: Damaging the enemy has 75% life stolen but split amongst all party members until the effect is overcome
*These effects could also have negative penalties given to the foes until the effect is overcome, such as:
**Water: -20% quickness, -20% crit, -20% evasion/armor
**Shadow: -40% evasion
**Earth: -40% armor
**Air: +20% chance to be crit
**Fire: Periodic Damage
**Light: -40% crit
So in this example, you could send a fire Sylesti in stage 1, try to do as much damage as possible, then send a more standard earth/air/light team. The enemies would all have periodic effects on them that slowly combusts to dealing aoe damage, which could be triggered by attacking them.

Tool 3: Async Multi-Stage Encounters
Now, you would be able to possibly enter into a Group Multi-Stage Event with other Players. People would all choose to enter the event and (presumably) have already selected their Entourage. Once begun, each stage of the Multi-Stage Event would be done in order and would wait for everyone to finish that stage before progressing. As such, each stage would have a time limit, after which point Players who have not finished the stage forfeit all rewards, are removed from the Async, and have their slots automatically "succeed" in some way. The time limit either would be something semi-long (like 24 hours * stage number) or be something the Player team could set if doing some sort of pre-arranged game. Once everyone has finished a stage, it automatically progresses to the next stage for all Players (and no one forfeits this way). This makes it so that if all Players are especially quick, all Players get to work on the next stage. Limits for stage 1, 2, etc, would be independent so a quick stage 1 would make stage 2 have "twice the time".
The crux of all of this particular tool is that when you do an Async Multi-Stage Encounter, you would have different Players doing different stages, but also have other corresponding sets of encounters per Player. So, if there are 2 Players, and 2 stages per Player, there are a total of 4 battles (Player A does stage 1 for Player B, and Player B does stage 1 for Player A).