STEP SEVEN: HEIRS OF FATE
From here, we have a large time skip after Birthright and Conquest. Heirs of Fate does not take place in the Revelation timeline at all.
Years after the war behind Hoshido and Nohr have come to a close, the kingdoms are at peace. There are two timelines, one where Hoshido won the war and one where Nohr won. These timelines branched off at the Branch of Fate where Corrin made their fateful decision that altered the course of the war for both sides in the fighting.
All of the major fighters in the wars have settled down and had children. In the case of the royals, they are being groomed to rule the kingdom. The others are just receiving a regular childhood since the war is no more.
However, this all changes one day when invisible soldiers appear for both sides. In Birthright and Conquest, the invisible soldiers never passed on into the afterlife since Thalone still lives in Conquest. Thalone's immense power had the timelines close enough that he could impact the one he wasn't from, Birthright. The soldiers overwhelm all the fighters, killing those who fought in the first war.
Why did it take so long for the soldiers to take their revenge? Thalone knew that he had lost the war, but since he was badly injured in the fighting, wouldn't have his immense power back for quite some time. It was enough time for the soldiers to settle down and begin the rebuilding effort, forging families in the process.
The soldiers appear and attack those from the war because Thalone wanted his revenge on both kingdoms since he didn't have his chance all those years ago. In Conquest, since he survives, he uses his power to reach into the other world and attack the people who survived over there.
The fighters from the wars ended up being killed in the fighting, so they sent their children away to safety. The children were split up into four groups depending on their timeline and who ran into them.
The first group comprises of female Kana (F!Kana for the sake of abbreviation), Kiragi, Mitama, Selkie, and Hisame. After explaining their pasts in a hurry, they are assaulted by invisible soldiers. Somehow, the group manages to fight them off using the weapons that they were given by their parents during the chaos earlier on. After the fighting, a mysterious young man (Shigure) appears before them and asks that they help him defeat the one responsible. The group agrees, wanting to know what is going on. Shigure takes the group to a safe spot just outside of Valla before disappearing, saying he has other people to find.
This Shigure is the son of Conquest's Azura, who only disappeared after the war instead of dying. She did, however, later meet her end at the hands of invisible soldiers when Shigure was young. Afterwards, he began to travel around, searching for more information about the invisible soldiers. He is guided by a small journal written by Azura before she died, detailing the war and Valla, which she went to a few times before settling down and having Shigure with an unknown man who died when Shigure was young. This was when Shigure found the large quantity of jewels with the power of transportation mentioned in Hidden Truths since they were detailed in the journal. Upon picking one up, he finds himself in the middle of the fighting on the Hoshidan side, a timeline which he doesn't know. He explores before finding F!Kana and Kiragi's team. When he leaves, he's intending to find the Nohrian royal children mentioned in the notebook (since Azura had heard of Siegbert and Forrest's births before her demise), though this doesn't happen until later on.
Shigure ends up finding a few others not long after. He runs into a small force being led by Shiro. The other members are Asugi, Midori, Caeldori, and Rhajat. After helping to rescue them, Shigure takes them to the same spot outside of Valla where the others are. Shigure briefly enters Valla and finds the jewels used for transportation and provides one to all the others, realizing that if he wants to find the Nohrian children that were mentioned in his mother's journal (since Azura had heard of them before her demise), he'll need to use one of the jewels once again. The group crosses timelines.
In the Nohrian timeline, M!Kana, Forrest, Nina, Ophelia, Sophie, and Dwyer all cross paths. Things aren't going for them since their parents were all killed by the invisible soldiers. After fighting a few of them off, they are met by Shigure and the Hoshidan fighters. Shigure realizes that they are still missing the Siegbert character mentioned by Azura.
The group travels for a little longer before they cross paths with Siegbert, Velouria, Ignatius, Soleil, and Percy. All of them are fighting off more invisible soldiers. With the help of the newcomers, they come out victorious.
Now that all of the children are together, Shigure flips through the notebook and puts the pieces together. The invisible soldiers, she had learned, were being controlled by a man who once sided with Nohr during the war named Thalone. He had survived the war and was now in Valla. In order to stop everything, then the group would need to eliminate this Thalone figure that was responsible for everything.
The group heads into Valla, ready to defeat Thalone. While they aren't sure if their parents will return afterwards, they still need to right this wrong while they have the chance. Shigure and the two Kanas lead the group into battle against another faction of invisible soldiers.
These soldiers are in no way regular, however. They are the many puppets that have fallen under Thalone's influence over the year. These include Mikoto, Sumeragi, Ikona, Katarina, Arete, Rivalis, and Garon. Nobody in the army recognizes them, but the player (if this was a real game) does. None of the puppets recognize the group members either, as they were all dead by the time that these children were born.
Once these fighters had been defeated, the group heads forwards, ready to fight Thalone and win the day after all this anguish. They find Thalone in the Vallite palace and prepare to fight him, but they are met with a surprise that brings even more grief to the army.
All of their parents who had died were now reanimated by the power of Thalone and were prepared to fight their children to the death. Shigure told the children that their parents were no longer themselves and that fighting them would free their spirits from the control of Thalone.
The army took down their reanimated parents and then fought Thalone. The pair of Kanas delivered the finishing blow, sending out a shockwave of magic that has now dissipated into the air due to Thalone's death as well as the fall of so many of his puppets. The immense power reverses time back to before the whole incident took place, back when the parents of the children were still alive, but this time, Thalone and his puppets are gone permanently.
Back in the fixed timeline, the children all reunite with their parents, though none of them have any memories of the event due to the odd impacts of Thalone's power. However, fate dictates that one day, they all will meet in one timeline, together and happy for the rest of their days… But for now, only a large and unexpected revelation will be able to tell when.