How you would written Avatar Arc??
The thing about the Avatar arc is that, if I had the choice, I wouldn’t have it at all. I consider it a waste of time because it accomplished nothing except getting the team back together, and tying off the “Gray kills Frosch” plot in the most unsatisfying way possible.
If it were up to me, I’d have used that space to establish what the council’s been doing and how they’ve reformed, using Natsu’s cluelessness to explain what happened and also use it as a way for him to realise that while he was gone, things had changed drastically. I would also focus on how the council is stretched thin dealing with both the rise of dark guilds and the looming Alvarez invasion that they can’t deal with.
Gray would probably be missing, hunting down END by tracking Zeref’s demons, and eventually cut off all ties with his former allies because he was tracking one close to Alvarez’ territory and he couldn’t afford to provoke Alvarez into attacking. Natsu goes chasing after him… as expected, and what basically ensues is a trip to an island close to Alvarez to hunt down Gray, only to discover that the demon he’d been tracking was actually the God Ikusa-Tsunagi - and it had been summoned by a Fiore dark guild. Once summoned, the god went on a rampage through the nation, killing most of the inhabitants and the dark guild itself, and then moved on through the island all the way into Alvarez’ territory. Natsu, Gray and co. try to kill the god, but don’t succeed in much more than slowing it down.
Of course, that’s when DiMaria shows up and reduces Ikusa-Tsunagi to a withered pile of bones in the blink of an eye (with timestop God Takeover shenanigans, clearly, but no-one knows that), and as the team watches in terrified awe, she declares the devastation, caused by Fiore mages, constitutes an declaration of war.
Cue Natsu and co. getting the hell out of dodge, and cue the Alvarez arc.
Naturally this sets up a different kind of Alvarez arc than before, but I’d do that anyway.