I'm upset, we will never get a true BW adaption. The finale of BW1 would have really cool to see in the anime. Amazing great set pieces: 1. N defeating Alder! 2. Gym Leaders fighting the sages. 3. Ghetsis taunting Ash's ability to be a hero. 4. Ash and N's fight. 5. Ghetsis's fight! 6. N's farewell!
This finale will be about ASH, primarily, as N wants to fight Ash and see whos beliefs survive!
You can keep Iris and Cilan, and have them fight the grunts and sages off with the leaders.
They will reassure Ash that he is in fact worthy of being recognized as the hero of truths, and Reshiram will see his strong truths to protect the world that he values so much. Showing to the audience, that they 100% believe and trust Ash to win and bring an end to Team Plasma.
However, after this Ash and Pikachu are alone.
Ash will meet N's foster siblings, Anthea and Concordia that tell Ash that despite N's actions, his heart is actually innocent. However, there is no more innocent than innocence. Talking about how Ghetsis picked their little brother purely for the purpose of being king, as he has pure heart, and could awaken the Zekrom but Ghetsis couldn't. This will make Ash question which side are they on, by telling him this.
With the sisters saying, "Whatever side that makes Natural, the most happy." and Ash just leaves in silence.
Ash and Pikachu will see N's room might feel bad, but they ultimately knows he needs to be stopped.
Ghetsis will stop Ash as he does in the game and talk about how N is practically unbeatable and that there is little hope for the world.
He verbally doubts that Reshiram would ever side with someone like Ash, he is a NOBODY and a LOSER in Ghetsis's eyes. Ash is a simple traveller who can't win mere league competitions. However, he will let Ash try since he does have the Light Stone and N wanted to fight him. Truthfully Ghetsis, does not care about N's wants about settling this as equals, but he just wants to see Ash lose all hope, like Alder did.
As Ghetsis says in the games:
"Go! Onward!"
"Discover whether you have what it takes to be a hero!"
Ash will likely reply as he enters:
"I know the truth. People and pokemon uplift each other."
"My many adventures have shown me this. I met others that love their prized pokemon, more than you could ever imagine."
"If I want to achieve my dream of being a Pokemon Master...that means I have befriend Reshiram and I will do that by staying true to myself!"
Ghetsis would be a bit startled by this answer, but he would keep his cool, since he doesn't see Reshiram responding yet. So for now, he is still confident that N will win. So he allows Ash to go ahead and to his King.
N would then rise from this throne saying that he has been waiting, but he is glad to see Ash has finally made it here. He wants to know for sure, who is right and who is wrong! Saying his desire is absolute!
N would then notice that Reshiram still has appeared yet and would get disappointed in Ash, since through his many fights with him. He genuinely thought his pokemon loved him, from his first battle with Pikachu, that Ash was different. Though it appears he was wrong and that he was kidding himself, the idea of bonding with pokemon through battling is still absurd to him. He brings Zekrom here, and gives Ash two options:
1. Run away and keep his pokemon safe, surrendering them so they can finally be freed.
2. Fight him and have his pokemon be senselessly harmed, fighting for what he believes.
Ash is a bit startled but, remembering how people are counting on him, he stays. Saying true to himself.
The Light Stone feeling the convictions of Ash would FINALLY respond to his truthful heart and Reshiram would appear before him. Ash befriends it quickly and it aids him in this fight.
Now with Reshiram, Pikachu, and Ash's other 4 pokemon, they end up defeating N's team and Zekrom. Finally making Natural understand the truth and he has an apathy. It's not about rejecting ideas or beliefs but rather learning to accept them. Believing that things can more than just Black and White, that there can be grey. He believes now, that this is true chemical formula to change the world for the better.
After N's change of heart, Ghetsis storms in angrily and dehumanizes N and says that he is mad that they even share a last name. N just lost someone as pathetic and young as Ash. Regretting even taking him in. Then Iris and Cilan walk in with Alder, and they hear about Ghetsis's true plans and that now know this was just an excuse for Ghetsis to rule the world.
Ghetsis realizing they ALL know about Team Plasma...as he says in the games:
"This doesn't change my goal. My plans have not been disturbed! In order to rule this world utterly, in order to manipulate the hearts of people who know nothing, I will have N be the king of Team Plasma. But, for that to work, you-- since you know the truth-- You must be eliminated!"
Ash would then fight and beat Ghetsis. He is angry about this, since he lost to a nobody from Kanto. Which Ash would correct likely say his catchphrase,
"I am not just from anywhere in Kanto..."
"...I am Ash Ketchum from Pallet Town."
Ash and Alder would forgive N, for being puppet in this whole thing, as he was raised from infancy to be Ghetsis's pawn. N would be confused and then Ghetsis would use this time to say it's impossible to reason or talk with N since he is "A freak without a human heart". Implying he knows nothing about being truly human. Only about Pokemon. Ghetsis gets carted away by Alder, Cilan, and Iris.
Ash would still want to talk to N, about what Ghetsis said was not true. That is more human than he thinks. Which would prompt N's whole final speech about, Ash's dreams of being a Pokemon Master and that he believes that he anyone could do it, it would be Ash.
N then jumps on Zekrom's back and takes off. However Ash follows him for a bit on the back of Reshiram, and then after after a bit of flying. N thanks Ash, since now he is going to see the world and enjoy it for what actually is. Rather from a jaded view. N says farewell to Ash!
After this I would imagine Ash would take Reshiram down to where everyone else is and then thank it for it's help. That he had fun with it but he can't keep it, but he will be sure to visit one day again, if Ghetsis ever returns (teasing possibly a BW2 adaption with Black Kyurem vs Reshiram) and he needs to step up to beat him. Reshiram respects this discussion and reverts back to being the Light Stone.
Ash returns the Light Stone to Lenora and asks her to take care of Reshiram, even when it's still like just the Light Stone. It helped him to save the world from Ghetsis's nefarious plots.
Definitely there is a celebration in Ash's honor and the story arc comes to a close, with the ending theme playing. Appropriately, called, "Onward to Our Own Futures" for Ash and N.