What's some theory that reads like a story with a main character?

The Autobiography of Malcolm X is precisely what you're asking for. It's an important read but also just a fantastic read...like it's genuinely very entertaining. It's written verbatim from recording made by the transcriber within like a month of his death and it's a full life story and although it's a direct transcript, it's very novelist anyway

Edit: strictly speaking though, no. There are biographical works that will involve theory and teach some. But strictly speaking, you're not reading theory, you're reading a biography. A text of political theory is the kind of text that doesn't really have any characters. It's kinda like asking for a math textbook with a main character.

In Dubious Battle by Steinbeck is a novel about someone becoming radicalized by the cruelty of the owners to become a communist organizer.

Bullshit Jobs by Graeber has a very distinct voice, with it either being Graebers reflections on his own life, or him responding to letters people have sent him about their experiences.

The Michael Parenti lectures are great too. All free on YouTube. Usually he's speaking at a lecture and reading some excerpts from his new book. His signature is that he always has a problem with the mic and complains about it in very Italian American fashion. Very witty and spirited. I find Parenti endlessly charming. I kind of love that man. Just pick a lecture you like the sound of, and have a watch/listen. They're reposted unofficially on Spotify under 'Not Michael Parenti'. I'd recommend the ones where he talks about movies and media to start with - they're the most joke filled, and pop-cultureish, which makes for easier listening.

Kropotkin's "the conquest of bread" reads super easily, it's super inflammatory, and has some very good points of theory. It's on YouTube on audio format

Grapes of wrath has interlude chapters which describes marxist concepts. I think the archive of marxist texts online has a few excerpts saved there.

Here's a PDF

https://ca01001129.schoolwires.net/cms/lib/CA01001129/Centricity/Domain/270/grapes_of_wrath_john_steinbeck2.pdf

how has no one mentioned "10 days that shook the world" by john reed??? Absolute page turner

It’s not exactly what you’re asking for, since it doesn’t have a main character and it’s not theory, but Mieville’s October reads like a novel and it tells the story of the Russian revolution. Worth a read since it’s educational and a fun read. Aside from some lame anti-Stalinism at the end it’s solid imo.

Unironically, Trotsky's autobiography "My Life" is heavy on personal details and relatively light in theory while also going over the entire Russian Revolution. Obviously he comes from a unique perspective which you might not agree with, but his overall depiction of events leading up to the creation of the USSR is pretty accurate. And Trotsky 100% writes like he is the main character, so it will probably fit your needs. https://www.youtube.com/watch?v=4v3YxJpw8KI

Ever heard the one about the coat maker and the ten yards of linen?

the first that comes to mind is chernyshevsky's "what is to be done"

Also not theory, but This Soviet World and Soviet Democracy and Russian Justice kinda do that.

Does "The Motorcycle Diaries" count?

The Jungle

There's a comic called Red Rosa which is a pretty good summary of Rosa Luxemburg's life, it's not particularly theory dense, but it is Marxist and goes into some stuff lightly.

Quite dry but a lot of Engels early work is done sort of like an account, where he visits a place and reports the facts and how he felt:

You could title this 'Engels goes to England!'

https://www.marxists.org/archive/marx/works/1845/condition-working-class/ch08.htm

'Ten Days That Shook The World' is good too - an account of the Russian Revolution from an American socialist who watched it all happen.

Maybe Stalins Shoemaker ?

[...] Let us take a shoemaker who owned a tiny workshop, but who, unable to withstand the competition of the big manufacturers, closed his workshop and took a job, say, at Adelkhanov’s shoe factory in Tiflis. He went to work at Adelkhanov’s factory not with the view to becoming a permanent wage-worker, but with the object of saving up some money, of accumulating a little capital to enable him to reopen his workshop. As you see, the position of this shoemaker is already proletarian, but his consciousness is still non-proletarian, it is thoroughly petty-bourgeois. In other words, this shoemaker has already lost his petty-bourgeois position, it has gone, but his petty-bourgeois consciousness has not yet gone, it has lagged behind his actual position.

Clearly, here too, in social life, first the external conditions change, first the conditions of men change and then their consciousness changes accordingly.

But let us return to our shoemaker. As we already know, he intends to save up some money and then reopen his workshop. This proletarianized shoemaker goes on working, but finds that it is a very difficult matter to save money, because what he earns barely suffices to maintain an existence. Moreover, he realizes that the opening of a private workshop is after all not so alluring: the rent he will have to pay for the premises, the caprices of customers, shortage of money, the competition of the big manufacturers and similar worries — such are the many troubles that torment the private workshop owner. On the other hand, the proletarian is relatively freer from such cares; he is not troubled by customers, or by having to pay rent for premises. He goes to the factory every morning, calmly goes home in the evening, and as calmly pockets his pay on Saturdays. Here, for the first time, the wings of our shoemaker’s petty-bourgeois dreams are clipped; here for the first time proletarian strivings awaken in his soul. [...]

Read the manifesto comrade. The characters are the different classes in the progress of history.

The manifesto

Bonus: the 18th Brumaire - anti hero the bourgeoisie

Unjust Depths

Harry Potter

And yes, the permaban was worth it.