Funnily enough, now that the OS arc draws closer I'm actually starting to think about the Tenrou arc more.
Here is what I assume will happen : Zeref will be on Tenrou Island during the trials despite Acnologia knowing that it's a regular haunt of his, either because A) Acnologia went days/weeks before to check Tenrou, before he went into hibernation, but Zeref wasn't there at the time and arrived in the meantime, or B) Zeref lost track of time. (Or C) he somehow decided this was an appropriate time to see Natsu - to be fair Tenrou does protect FT members from death...) Now the interesting thing to think about is who will figure out that Zeref is on the island, when will they do so, and what will they do with that knowledge ?
The "who" obviously depends on who will take part in the trials, be it as examiners, candidates or partners. For the candidates : I assume Natsu, Gray, Mest, Cana and Levy will still take part. Freed and Juvia's circumstances are a bit different from canon due to the Battle of FT not happening, but I still think they'll be nominated (actually maybe Freed was already a candidate in X783?). Elfman won't be there, but I'm actually thinking Erik should be a candidate (I'm actually not sure why he hasn't been yet - is he asking the master not to have him complete with his siblings for the title? Does he not want to be S-Class for some reason? I would have assumed Erik would be nominated before Natsu or at the same time, not after). As for partners, Happy, Loke, Lucy and Bixlow will most likely accompany the same candidates as canon. I guess Lisanna might go with Juvia again, but you might also have Juvia develop some new friendships. Actually I think a Juvia and Evergreen team might be nice. Bonus if they fight against Erza in the first round. Erik would go with Cubellios (or maybe with Wendy, if your unison raid art was related to that arc, but I don't think he would 'cause Sting (and Rogue) would be jealous). So the most uncertain partners are those with Mest and Levy. Mest might not be able to use the "Mystogan's pupil" excuse again, given that Mystogan is less of a loner here; that plus her protective elder brothers has me doubt he would ask Wendy. But it's not like I have a better idea for a partner either. As for Levy, well she might go with Jet or Droy, but she might also pick Lisanna, if Juvia goes with Evergreen? I feel like their proximity to the dragon slayers probably made them better friends than in canon. Finally, for the examiners, I'm assuming that Mystogan will be in Edolas and Acnologia sleeping, but that Laxus, Jellal, Gajeel, Erza, Mira, Gildarts and Makarov will all come. Mira could stay behind this time, but I'm thinking she won't. They might also bring Wendy along for emergency treatment if she's not Mest's partner (though I don't think they usually bother, so maybe not).
Now my assumption is that the trials will be the same as canon. So first the S-Class examiners come to the island. Gajeel might be able to tell that Zeref is there (dragon senses + having encountered the guy a couple times), or maybe Laxus, but it's not a given. Also I'm thinking that the magic of the Tenrou tree/island might be overwhelming enough that it partially hides Zeref's presence. Then, all the way from the ship, I don't think that Natsu or Erik, who might have a better chance at feeling his presence, would be able to tell (especially behind motion sick). Trial starts : Mests teleports with Wendy, Freed throws up a barrier, Levy and Evergreen rewrite it. Mest, Freed and Levy pick the same routes they did before. Juvia now has an option that was closed last time - the Mira route, though here it's Gajeel waiting instead. For fun, they go the Erza route again. Then comes, in order, Natsu, Erik (or maybe Erik then Natsu?), Gray and Cana. Natsu being less fight oriented, might not pick the E route again (where Laxus is waiting). Or actually, he might go with "G for Gajeel" and fight Freed and Bixlow. Erik, hearing people and thus knowing the options between fighting Laxus / fighting Mest and Wendy / fighting Gajeel, would probably pick Gajeel. Then Grey and Loke go against Mest and Wendy, Lucy and Cana against Laxus. (Damn, actually maybe Gildarts should still fight - no, it makes no sense unless there's extra candidates, he's overpowered). Anyway, everyone is focussed on the first task so most likely not noticing Zeref. Except maybe Erik.
Other option : rather than keeping the same structure as canon (3 fights with S-Class mages, 2 duels, 1 lucky road), all 6 S-Class mages are possible opponents, + 1 or 2 lucky roads (depending on if there's indeed 8 candidates, since I'm not really sure all of them will participate), or Acnologia also comes along and it's 7 S-Class fights + 1 lucky road. I might actually like that option better, it also gives GH a real reason to use the Dragonsgrave pollen, but then Acnologia would sniff out Zeref immediately so there's that downside.
Anyway, back to my first theory, Gray and Levy obviously pass. I would bet on Natsu passing, but in essentially a 2 vs 1 fight (with Freed having the time to write rune traps) it might be a difficult fight. Juvia probably fails, Cana might pass against Laxus for the same reason Natsu passed against Gildarts. That or they outsmart him and use transportation against him, but I wouldn't bet on it. Cana failing in the first step would be very ansgt-y, and a good reason to have her and Lucy wander around the island because she doesn't want to be go back to the camp where the S-Class mages (including Gildarts) are. For Erik I think it will depend on whether he is actually trying to make it to S-Class or not (similar to Jellal previously), and/or if he has something to prove against Gajeel for some reason.
So for the second task : Gray, Levy, Natsu?, Cana?, Erik? are qualified. Mest and his partner wander around the island, Juvia and Evergreen go back to camp. There's the question of whether Freed and Bixlow leave like they did the first time - but back then it was with Gildarts, who in my version has yet to play a role in the trial, so it doesn't make much sense. Laxus and Gajeel (and possibly Erik if he fails) being dispatched the find the wayward Mest (and Cana?).
So who finds Zeref first, during the second part of the trial (which might be modified so that Gildarts / Mira / Jellal have a role to play, or they're part of the 3th challenge) ? Well, canon events would say Natsu. I'll argue Erik will either find him first or hear Natsu finding him and come to check on the situation and/or warn one of the examiners (Laxus/Gajeel/Mira). Another option, if they get eliminated, is Lucy and Cana, just, Because. Obviously Natsu arrives before they get - well, killed, as much as is possible with the Tenrou protection. Question is, at that point, does Zeref leave? I would say yes, but he didn't in canon... then again the context was different. It would be fun if Natsu / Erik took advantage of the situation and asked where Mavis' grave is XD.
Then GH arrives and all hell breaks loose. They're looking for Zeref who isn't on the island anymore, the dragon slayers except Erik get taken out by Dragonsgrave pollen, Fairy Tail is panicking over Zeref supposedly being on the island but for different reasons, and some secrets probably get dragged up in the process. Plus the Mest/Council stuff. (I wonder if they would try to fire Etherion on the island as is threatened in canon. It would actually be pretty fun to have Etherion fired only for Acnologia to block/eat it. A bit less fun but also interesting would be for Etherion to be the reason Fairy Sphere is used - with Acnologia, Sting and Rogue being left behind in the 7 years skip. Hopefully that wouldn't kill Loke.)
Anyway, definitely lots of potential with this arc as well!!!
Fascinating, I love seeing people guess ahead. You got a few things, but I won't say what lol.
I will answer one thing though, because it has come up a few times, but really the main reason Erik isn't S-Class is because he doesn't want to be. (Does this make him a tiny bit of a hypocrite after Jellal's trial? Perhaps lol, but that's part of the fun.) Not really for self-loathing reasons though, but mostly because he thinks it'll be a huge hassle because of the popularity aspect. (Aka Mystogan's biggest regret lmao.) He's avoided getting nominated at all so far because the people who know him know he doesn't care and from a larger perspective (like Makarov's), he doesn't really do much as far as solo quantifiable jobs go. At least not enough to make it known. (He can do some ultra-impressive group takedown for a job and come back and downplay it so well lol.) But. Lately Erik has been impressive on main a bit more, so :)
