In my opinion, the film tells a story of responsibility and abandonment.
The fox father gave up the freedom and desire of being a beast because he took on the responsibilities of being a husband and a father.
To become a real beast, you have to give up, give up warmth, give up stability, but have freedom alone.
Is there a way to get the best of both worlds? Maybe not.
But there is the next best thing—to pursue one's own heroism within the limits of responsibility.
It’s not the saddest thing to be the next best thing. The saddest thing is that you don’t even know what your own desires are, and you can never become a real beast.
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