My project ends up having a fairly large party as the game progresses (possibly around 10 at the maximum, details uncertain though), which means most of your characters don't get a chance to do anything. Sure, they can swap out, or apply healing and the like on the map, but it doesn't feel great to have potentially more than half the party just tagging along for the ride while barely contributing.
So I was wondering what would need to be done to create a system where reserve actors (as in, non-battle members of your party) can hop into the battle, use a skill, and hop out again, generally in response to some specific trigger in the fight. For example, if you score a critical hit and nearly kill an enemy, one of the reserve actors might hop in and finish it off. Or if you gain a preemptive attack on the enemy troop, a reserve actor might hop in with a party buff. Maybe if one actor protects another and is left with very low health, an actor will hop in to heal them. The general idea is that they interrupt the normal flow of actions to insert a new action, then retreat.
For the curious, the idea for this came from the 3DS game Radiant Historia: Perfect Chronicle. I'm not aiming to replicate its battle system in full, though - I just want something that will let the reserve actors play a bit more of a role in battle.
Note: This is not a plugin request, but rather a query of what I might need to do to implement such a plugin (well, unless one already exists). I don't use any Yanfly plugins related to battle. I do use SRD_SummonCore, which is similar in the sense of adding additional actors to the battlefield, though I don't currently see any way it could help with this idea.