It is a cruel expression to capture enemies and brainwash them into becoming your friends, or to dedicate unwanted units to the evil gods.
However, something similar to this has already been done in Pokémon and FEH.
Those are just a little safer expressions, avoiding direct expressions.
Essentially, what they are doing is the same.
In the plot, the evil god was going to be Lopto, the Loptous from FE4.
Lopto, an evil dragon of the Earth Dragon Tribe, was banished to another world for his hazily evil deeds.
Meanwhile, the dark priest, who was studying heretical dark magic, had escaped from his pursuers and fled deep into the forest.
As he is driven deep into the forest, Lopto happens to be beamed there.
The dark priest worshipped Lopto as a god for saving him from danger.
Lopto learns that in order to return to the original world, he must destroy the four temple jewels (MacGuffins) in this world and gain their power.
Therefore, Lopto plans to destroy the four jewels by using the Dark Priest to have him attack the countries.
To do this, he gives him the art of brainwashing and the Dark Bible.
Eventually, with the destruction of the nations and the destruction and power of the temple jewels, Lopto returns to his world.
At this time, the Dark Priest is either abandoned or dies as a sacrifice.
Returning to his original world, Lopto meets his friend.
"I heard you were banished, but have you returned yet?
"By the way, there’s this strange person named Galle who’s been coming to this dragon village.
“You like that sort of thing, don’t you? Would you like to meet him?”
And so the story continues to FE4.
One problem is that it is very difficult to draw conversation scenes because the main character works differently as a bad guy.
I think the Start Event and End Event scenarios will be quite difficult because they are attacking for their own good, not for justice.
Partly because of them, this idea was frozen.