I'm just starting to work out a story right now. This story actually has two MCs. And for a significant portion of the story, they will be the only two characters.

The way it looks right now, I'm thinking of writing the story in two parts. Part One almost entirely from the POV of the male character. Part Two, following Part One chronologically but almost entirely from the POV of the female character. I'm not sure whether I would have a Part Three, sort of a Coda, from the male POV again or not right now.

I can see where that initial shift of POV is going to be disorienting. I mean, you've been following A through 30 or 40 thousand words and all of a sudden, wham! who's this? Because B won't even be in the first half of the story at all. There may be ways to cushion it, but there's probably no way to avoid that disorientation completely.

The way I've seen this done that actually worked was to have the sections of the story be some form of communication between the two characters.

One feature of dramatic structure that's preeminent to a plot is Unity, unity in causation, tension, and antagonism, unity in character motivations and predicament. Less complex stories have one focal character, one predicament, and a single-minded pursuit in addressing the predicament.

Another double focal character type of story has a false protagonist/true protagonist relationship. A false protagonist carries the front-end action and the true protagonist the back end.

I see several complications in unity from having two different, exlcusive protagonists in two different sections in one story. Do they have the same predicament. Do they have similar purposes and problems. Do they have similar outcomes. What unifies their individual stories into one story. I think that as long as the question posed at the beginning of the story is artfully answered by the ending, a dual-protagonist story can work.

An example of a false protagonist/true protagonist situation, a detective struggles to solve a murder. Identifying who did it is the answer to the most important question posed by a mystery, Who Done It. The detective's purpose is to solve the murder. The detective's problems cause setbacks to the investigation. So he's the character in first position.

The character in second position is related to the victim. The victim can't solve the crime, nor can the perpetrator, so she's logically in second position because she wants to see the crime solved but isn't a detective. She has motive, but believes she lacks means and opportunity to solve the crime. She's peripheral to the action. Until the detective abandons the investigation, she doesn't need to be on the stage except for Unity's sake. Her relativity in relationship to the predicament and the victim and throughout the investigation, her relationship to the detective are important.

In order to maintain unity, as the earlier section draws to a close, she becomes more involved in the investigation and rises in preeminence as the detective falls. She becomes the true protagonist and moves into first position. He could abandon the investigation because he's weak, incompetent, frustrated, or co-opted and be completely unessential from then on, except answering why he dropped out asks again the same question of who done it. The detective being co-opted would probably be most dramatic because his change of fortune or circumstance goes completely from good to bad. His failing nobility readily incorporates his other failings.

Readers will still want to see the crime solved. A gradual transition ending with his abandoment of the case and her taking it up would not necessarily be disruptive to answering the question. So she becomes the one to solve it in the second half, with little or no involvment by the detective. However, when the crime is solved, she also uncovers the why answer posed by the detective abandoning it, say, the perpetrator coerced him to quit. The same question, more or less, reasked and intensified at the close of the first section answered at the ending. Violà! unity.

Edited to add; The detective dropping out in the middle becomes a setback for the true protagonist on top of the detective's setbacks that have occurred up to that point. Then her efforts and setbacks in solving the murder escalate from passive involvement to active involvment to climax.

The first part of the story, in A's POV is his rise and ultimate failure. A is a VERY long-lived character, BTW. B can't be in this part of the story because she hasn't been born, yet.

When A has basically become a hermit, B's story starts and then intersects with A's. Both of them end up having the same goal--or very nearly--and working together to achieve it. B couldn't do it without A. A wouldn't even try without B.

The twist in this case is that A, theoretically, could do anything. A is inspired by the idea of the Greek gods Heracles and Aeclepius--both children of a god (Zeus or Apollo) and a mortal woman. Both became gods when they died by fire, which burned away the mortal part. This is the basic idea for A, except becoming a god doesn't come with an instruction manual and he screws it up. He keeps trying to relate to the world the same way he did when he was mortal and makes a mess of things until he just gives up. Obviously, there's more to it than that, but that's the jist.