The Swaps

Alphinaud == Alisaie
Cid == Nero
Th'ancred == Y'shtola
Urianger == Moenbryda
Aymeric == Estinien
Lucia == Livia
Regula == Zenos
Hien == Yotsuyu

Pre-Canon

Th'ancred, of the S tribe, challenged their leader and lost. Still feeling cocky, he left them. He was still a kitten at this time - still very young. He left with his brother, and hoped to attract ladies. (This, of course, was a failure - and he was still taken in by Louisoix. This time, however, for his mix of sneaking and magic prowess.) Yes, Th'ancred was young-ish when this happened. You complete dumbass of a Miqo'te.

Before the Calamity, Urianger was left in Sharlayan for his knowledge deciphering prophecies was still needed by many there. And Louisoix needed somebody with that mind to help take care of Alisaie and Alphinaud, should he fail... and Urianger took that seriously, even as he felt so angry and useless. (He went to Eorzea with them.)

Meanwhile, Cid Garlond failed in fleeing the Empire. Instead, he was taken into further to the Empire, Gaius refusing to let him go. That strength that helped him try and flee made him worthy of life, but...
Meanwhile, Nero Scaeva took the chance to flee. But not out of disloyalty, but instead to see if he could infiltrate Eorzea himself. (It was only later he was dis-owned by Garlemald. He still doesn't believe he was.)

There's a lot more to put here - why certain people took certain paths - but... it's a LOT.

Seventh Umbral Era (2.0)

Only differences from canon will be noted. The Warrior of Light... well, to make it easier, they did the Gridiana opening, just so don't need to deal with the swaps in those storylines.

However, the first big difference does come before that, in the caravan in. Urianger wasn't talkative, but he was there. One twin on each arm. It was adorable.

Anyway, when dispatched to Thanalan, Y'shtola came with the Warrior of Light. She told them a lot about the theory of Primal, and how they work. However, the Warrior of Light still had to face Ifrit alone. During the fight, strange lazers seemed to also strike at the Primal. This was the work of Cid tol Garlond - who didn't just take readings. Instead, he also wished to see how fragments of the power of Ultima would harm the Primal.

Inconclusive. Thankfully, the battle was too chaotic, and the Warrior of Light didn't find out about this man.

When joining a Grand Company and going to the rememberances, Urianger was still with the twins - and still quiet. Reciting a prophecy, and leaving with them. The two do split, though. Alisaie realises that even if she doesn't like organizations, she can learn of what happened around the Calamity better if she tries working with them. Meanwhile, Alphinaud is disgusted at the Grand Companies and longs for something more... neutral. Urianger has trouble deciding which twin to go with, but he eventually goes with Alphinaud. Alphinaud needs more people with him. But Urianger wishes he could help them both... his heart longs for it.

After the Sylph quests, Minfilia is a little surprised Alisaie is the one asking her how the matter of Sylph and Ascian is going. But she suspects this has to do with the Calamity. If she must play the part Louisoix did, then she shall. But Alphinaud insisted he knew a better way, and so he's off. (Alisaie doesn't mention that Urianger is with him - she is unsure of the relationship that Urianger shares with the other former Archon.)

The Ala Mhigo/Hakkue arc goes around the same. Including Th'ancred getting a necklace with a Dark Crystal... but, due to his use of his magic, he resists the control for a time. Though he can't say it's happening - his voice seems to go when he tries. So, during the Titan Arc, there Th'ancred is trying to assist the Warrior of Light while being reminded of his failures. That his brother had gotten lost in the Empire, likely dead. That he couldn't handle this all. He was a failure of a Nunh, and a complete idiot. And eventually, Lahabrea took over - Thancred vanishing sometime while the Warrior of Light dealed with U'odh Nunh. Th'ancred had gone there, but that's what got to him...

So, yes - Th'ancred was still possessed by Lahabrea. This is also around the same time the Warrior of Light met Aymeric, the Azure Dragoon, for that questline. Though Aymeric is friendly, he still has to go on the run. Still stole one of Nidhoggs' eyes. (Somehow, this Warrior of Light is omniclassing everything. Just so the story parts can be included.) This also means that the Warrior of Light met Y'mhitra, and learned Y'shtola was a certain sort of information seeker. She used magic in her stabbers - a Rune Knight.

Anyway. After the Waking Sands were attacked, the Warrior of Light took refuge at the church. It was soon that Alisaie burst in, and revealed that the amnesiac man staying there was Nero nan Scaeva. Nero nan Scaeva was a traitor - and he's just as sassy and angry as the canon Nero. Well, a little calmer. However, the Ishgard Arc is very amusing - with, you know. Alisaie and Nero bickering.

Seventh Astral Era (2.1 - 2.55)

TO BE ADDED

Heavensward (3.0)

TO BE ADDED

Dragonsong War (3.1 - 3.56)

TO BE ADDED

Stormblood (4.0)

TO BE ADDED

The Legend Returns (4.1 - ???)

TO BE ADDED