While this question seems daunting (or even impossible) at first, the tools to achieve the effect of your party members emerging from your main actor is already built into RPG Maker MV. It requires the creation of multiple events, one for the story event/dialogue itself, and one each for the other three actors in your party. Let's start with your other actors events:
Each actor event requires two event pages, and will share a switch for the purposes of creating this effect:
Rename all of your actor events to something specific, like their name and purpose, and name a switch to specify its use for this party effect.
Page 1:
- Check "Through"
- Set Priority to "Below Player"
Page 2 is identical to Page 1 except:
- Set events Sprite to the actor named in the Event Name
- Set Switch condition to your new switch
Now, set these actor events someplace out of the way, so they wont get cluttered up with the other events in the map. On to the actual story event.
For the sake of simplicity, I would write out the story event without the use of the party coming out first, just to get the narrative aspect of the event out of the way. After that point you can insert the other actors as needed.
For the sake of demonstration how you would go about it, I created an empty map, using the default new map settings, and did the eventing. I created four characters, the extra three characters being named Ciel, Markus, and Sandra. I created my actor events as above and just used switch 1 as it is, since this was an empty project otherwise. I then made the "story" event just have the player wait two seconds, then the other actors come out, face the camera for a second, then go back inside the player. This is what the event looks like in the event window:
Code:
Wait : 120 frames
Set Event Location : Cielevent, (8,6) (Direction: Down)
Set Event Location : Markusevent, (8,6) (Direction: Down)
Set Event Location : Sandraevent, (8,6) (Direction: Down)
Control Switches : #0001 = ON
Set Movement Route : Cielevent
: Move Left
: Turn Down
Set Movement Route : Markusevent
: Move Right
: Turn Down
Set Movement Route : Sandraevent (Wait)
: Move Up
: Turn Down
Wait : 60 frames
Set Movement Route : Cielevent
: Move Right
Set Movement Route : Markusevent
: Move Left
Set Movement Route : Sandraevent (Wait)
: Move Down
Control Switches : #0001 = OFF
And there you have it. The party members come out of the player then go right back into the player. play around with eventing some more and see what other cool stuff you can do this way.
--EDIT--
Forgot to mention that only the last item in each Set Movement Route routine requires the wait option checked, in the case of my example, the Sandraevent. Edited the code example to reflect this