I will give an introduction about the movie first, and then I will dive mainly in story element, so spoilers ahead

The Boy and The Beast
This is the story of A boy named Ren, who lost his mother in a car accident while his divorced father was away. And since he was the successor, he was meant to live in the family head's house against his will.
So he runs away, and find our friend Kumatetsu and he offers him to become his pupil, because that is one of the rules to become the lord of the monster world, which he intends to do. And with nowhere to go, and wanting to become stronger, Ren agreed.


# What are the two points of view

The story focuses mainly on Ren, kinda. Story-wise, it is. Ren is the one who was troubled first, he is the one who wants to become strong, he is the one who faced his fears in confronting his father, he is the one who found his love, and he is the one who defeats the villain in the end.
But that's not all! you could look at it that way, or flip it around. Ren was just our entry into the world of Kumatetsu, the one who wants to be the lord. It is about the troubles that he faces to become a lord. He does not know how to treat others, since he had no parents or a teacher to behave him. He is a monster, but not a bad one. He is good-hearted, but the world is against him, that is why he puts up the tough and strong face. It is obvious when Ren said that he would leave him to go and live in the world of humans, and he kept that strong look. When Ren actually left, he ran following him to try and persuade him. He is desperate for Ren.
Even though the story focuses on Ren in the build up and the obstacles, but the characters - mainly from the monster world - always compliment the growth that Kumatetsu underwent. And that is the great point in the balancing between two characters growth, in a short time span. And it is not displayed shallowly, as "look at how much Kumatetsu has grown", since a lot of monsters in different places note his growth, and we see it as well, but mainly through Ren. Since Ren and Kumatetsu are a lot like each other in their characters, we can see how much both grew by comparing them with each other. Since Ren is a "human", we can understand him better - this is a good way to present the changes for casual viewers, but they are not different from each other so even without Ren we could see how much he changed, but Ren strengths it.
So The secret is: Utilizing the world structure and characters in favor of Kumatetsu, while the obstacles and story for Ren. Since both of them have the same character, we don't need to focus heavily in both, we need one only, who is Ren. The main difference is that, Ren found Kaede, his lover, while Kumatetsu found Ren, his son. Ren was the person that changed Kumatetsu, so Kumatetsu can't live without him. That is why he "wanted to fill the hole in Ren's heart", to actually fill it and repay him, and so he can live in peace, since he is with him always. As for Ren, he found his lover, who stood with him even when he was barely able to read. She taught him, bought clothes for him, and more importantly, fixed him emotionally.
This is why I think the movie nailed the two perspectives.
A bonus: A great way to symbolize something and make it obvious to the viewers, but not stupidly obvious, is to tell them beforehand. What I mean is the whale scene. Earlier in the movie, Ren and Kaede talked about Moby Dick and what the whale represents - a mirror to yourself. So when Ichirouhiko turned into a whale, the audience should think "This might be like Moby Dick, and Ren needs to fight himself to defeat Ichirouhiko." and somewhat this is what happens.