Acnologia isn't in this story arc, though we fought/talked to zeref for a while a long way back.
I posted a recap of the story a little while ago. (page 18)
I'd suggest reading back at least that far.

Right now is kind off difficult since we are about to go to the spirit realm.
If booksmusicanime agrees maybe it would be interesting to play someone who lives in the spirit world?
Or you could have a connection with one of the other players characters and some way to communicate with them. (communication lacrima)
So they could ask for your help, especially if you are especially useful in the spirit realm.
Or then again you could also just show up like Sammy did. she just happened to be around.