You didn’t just ask THIS question. I’m going to spend the next hour writing this answer. I can’t believe you actually want to know omg
ok firstly let’s get some facts in case you don’t remember. My MU’s choice was to let Chrom kill Grima. Grima returned to his slumber, which left MY Grima with many doubts and worries about the future.
Grima is still there, still ready to come back and ruin everything. Since my MU didn’t sacrifice himself to save the world, he feels obliged to somehow ensure that his bloodline won’t fuck everything up again.
I imagine there are four types of people in Plegia:
1. those who didn’t like Grima but had to pretend they are Grimleal because they had to (like Gangrel)
2. those who were devoted Grimleal but opened their eyes when thousands of people were eaten just to resurrect this stupid ass hoe, probably having lost friends and/or family members
3. those who hold a grudge against Ylisse for the wars and side with Grimleal just for the sake of opposing Ylisse whenever possible; often being pretty passive about it, especially the younger generations and people who have the Ylisse hate set as a tradition in their family
4. Grimleal 4ever
Now, my MU at first goes to Plegia as Ylisse’s ambassador- to help with maintaining peace among people, assist Chrom during his diplomatic meetups, and helping with embracing the general chaos during the interregnum period. Since he is very passionate about politics and he has a thing for leadership, he was a perfect candidate for this task.
His job at first was supposed to be temporary and he was supposed to come back to Ylisse once Plegia gets a new king. He realized that it wasn’t actually a good idea to leave Plegians in hands of Grimleal again- since they still were there and still wanted to cause a lot of trouble.
His first idea was to completely dominate Plegian leadership with Ylissean, and to make Chrom maintain both countries, just to make sure that worshipping Grima was considered a crime and that there would be no one who’d dare to mess around with resurrecting him again.
Chrom of course didn’t like the idea of playing Walhart and trying to win peace through violence, so my MU figures he will have to do it himself- and came up with a more civilized plan, and gets it approved by Chrom ofc.
Firstly, he talked to crowds, quickly gaining a lot of supporters and a lot of enemies. But that was the plan- to make people talk about him in general, to make himself recognizable and to encourage people to even consider the idea of removing Grimleal from their lives entirely.
Some people join him because they want Grimleal to disappear.
Some join him because they think he’s the hierophant and they acknowledge him simply because of that.
Some join him thinking he’s Grima himself (well, his name IS Grima.)
Some oppose him, knowing well he’s here to wipe out Grimleal and that he’s a threat to whoever Grimleal wanted to take the throne.
Some oppose him because he was with Ylisse.
Some attempt to take his life, either because he’s a threat to Grimleal’s authority or because he’s a threat to the world (being Grima).
He leads people toward a safer idea of life and religion, and works hard on changing their mindsets. Of course he sometimes has to conquer some of the opposing regions. But he does that after claiming the throne. He can do that easily- because he’s the rightful prince. He has to kick everyone from the court though since they refuse him entirely, so taking the castle required force. BUT WITH CHERCHE AT HIS SIDE IT WAS EASY. Morgan probably wrecks everything herself haha.
He can’t become the king yet, he is just the prince.
Originally he planned to make Plegia’s religion illegal and replace their main god with Naga- but soon enough he realized most of the people wouldn’t like the idea, and that majority of the people just want to believein something. They aren’t dangerous, like Grimleal are.
So one of his first changes after becoming the ruler was to separate Grimleal’s beliefs from his own follower’s harmless beliefs. He claimed those completely different- and Grimleal were considered a dangerous sect people didn’t want to fear anymore.
After some time it turned out he wasn’t followed by people only because they acknowledged and accepted him as the new candidate for the throne- but also because they saw him as their ‘spiritual leader’, too. He basically became a god, but he always made sure it was harmless- and that there weren’t any fanatics among his people and among those who chose to stay loyal to the real Grima.
He still let everyone know he is against the real Grima and that he is indeed one with him- but refused to /become/ him. He didn’t like how people claimed him their almost-god, but accepted it and said that as long as people need it, if they need to believe in something and cling to their beliefs, then it’s okay and he’s here to help (so any requests to murder someone or destroy the world were refused ofc lol).
His main goal was to rid Plegia of fanatics and maniacs. And it took him years to accomplish it, while struggling with many other things (his own newborn children, people who didn’t like how lovey-dovey he was with Ylisse, Rosanne (of course he helped Cherche with it, what do you think), maintaining good relations with Regna Ferox and Ylisse, handling his people’s needs, uprisings etc.)
I have millions of ideas and I love to think about this stuff. What I just wrote is maybe 2% of what I should really write lol.
tl;dr he just went and took the throne to make sure his bloodline and his choices wouldn’t destroy the world in the future, because he felt it was his duty and that he owes that .
He sets a lot of new laws regarding Grimleal and worshipping THE Grima, and also sets rules and 'guidelines’ for his descendants. Somehow he has to tie his family with Chrom’s family to make sure they would always be in contact- just in case Grima comes back. They need to know what to do and how to handle shit, after all.
He has a lot of things to worry about and deal with.