Disclaimer: I don't play JP, I've pulled these from the wiki listing and individual threads. Obviously any of these could change for GL.

We've got event co-op sooner and people will probably want the rewards without the freaking out and stress that we've seen since day 1 of this event, and who knows how long 35CP weapons will take to make it easier without synergy. So if you're like me, and want to be prepping at least one of them to use in advance so you aren't dragging a team down, here goes:

For a bit of a key, I bolded the ones that are not out yet (but will be at the time). I also added italics to event characters, which some newer players might have already missed (or have a chance to miss). The non-event synergy characters will have been out from previous story chapters, or for the limited ones, I assume they will have come back in Lost Chapters at that point.

Random trivia: All story characters up to chapter 9 have been a synergy character at least once except for Lightning and Edgar. Huh. Meanwhile I see the best girl's in three so far~ Glad I leveled her up, wish I had her weapon though.

Another thing to keep in mind is that synergy also applies to gear from those characters as well, which you could put on non-synergy characters if you had to. Just in case you were thinking of certain pieces to max or pull for in advance.

If you're not planning to pull on some of the forthcoming banners, you may want to try and at least have either a synergy unit or gear representing them available for the co-op, at least until you start MLBing 35CP weapons and such to be able to brute force it.

And last, if you are going to plan to grab the event character and max them out asap, make sure to stock up on the crystals they need in advance, at least, and probably have a good 5* weapon ready of their type. This will be harder for weapon types we don't have ANY of yet, like spears, bows, and whips. Characters who use those:

And that about wraps up my browsing for now. If there's interest, maybe in another 3-6 months I can try to do this again and include newer events and anything else you guys have to add to this one. Cheers~