Do I need to finish the main story before doing Ex Decagrammaton episodes? I'd like to do the event but I haven't started the Ex deca episode or finished the final ep.

Friday night, time to resume our bluefes themed jigs Sensei.
https://jiggie.fun/millenniumexpoarchiv1
https://jiggie.fun/millenniumexpoarchiv1
https://jiggie.fun/millenniumexpoarchiv1

Please tell me the last day will be everyone welcoming Rio back.
Or do you mean to say that she still haven't gone back by the time the sewage lover appears again?