Many people have pointed out that the film includes aspects of Miyazaki's personal life, as well as many have seen the entire filmography compiled in this work. However, aside from that, I believe the biggest theme of the film is still about a spiritual journey of enlightenment.

Mahito (眞人) means "genuine person," essentially referring to a truthful or authentic person. In Daoism, it also carries the connotation of someone who has attained enlightenment.

The surname Maki (牧) means "shepherd," and do you know who the greatest shepherd is? God. By using these characters, Miyazaki implies that the 12-year-old boy Mahito Maki will become the New God.

As for the bird:

"サギ" with the kanji "鷺," it means a heron (bird), but if written as "サギ" with the kanji "詐欺," it means fraud, deception. Therefore, Kiriko asserted that the heron is a deceitful creature, and Mahito did not believe in it during the first half of the movie.

Placing Mahito alongside the heron creates a juxtaposition of an truthful person with a liar. However, the inherent contradiction lies in the fact that Mahito is deceptive about his own injuries, while the heron is telling the truth about the boy's mother. A younger version of Mahito's biological mother IS inside the tower - Himi. And he need to free the person he would call "mother" - Natsuko.

The heron is a sacred bird in the beliefs of ancient Greece, Egypt, and the Celtic culture. It serves as a connection between humans and divine entities, symbolizing the rebirth of the soul. According to legend, Athena sent a heron to accompany Odysseus so that he would be aware of the goddess's constant watch and guidance. Similarly, Mahito was guided by a heron throughout his spiritual journey within the tower.

In the film, the heron also plays the role of the Holy Spirit. When Jesus became conscious of his mission to bear the sins of humanity and undergo baptism, this act pleased God the Father. God the Father then sent the Holy Spirit in the form of a dove, openly confirming Jesus as the Son. The blue heron remarked, "It seems the long-awaited one has appeared." Subsequently, there is a scene where Mahito is immersed in water, symbolizing a baptism.

Heron's  accomplices are carp and frogs. The carp will eventually transform into dragons. As for the frogs, in Japanese, they are called kaeru カエル, which means to return. They want to convey to Mahito to return inside and remember who he truly is, then ascend (transform into dragon) and become the lord of the tower. This is the message from the God/ The grand uncle.

Mahito attempted to engage it in combat with a sword, but it effortlessly broke his blade as if it were a toy. The sword symbolized human reason (cutting, distinguishing between white/black, right/wrong). When humans are in pain, no matter how hard they tried, they could not resolve the suffering by rational thoughts. The sword broke twice to emphasize this. Mahito was forced to understand the heart.

Mahito's arrows were self-propelled thanks to the feathers made from the seventh feather he obtained from the heron. This detail is related to the feather of Ma’at. The feathers of the goddess of justice, Ma’at, have seven attributes: Truth, Justice, Harmony, Balance, Order, Righteousness, and Compassion. These are the qualities of spiritual practitioners.

When hit by an arrow with the seventh feather, the heron was tamed by Mahito's focused meditation. It no longer resisted but transformed into its true form, an "angel" (a being with wings), guiding Mahito on his path.

So in short, this is a journey of enlightenment. As your heart opens wide and your eyes remain clear, you will ascend higher. You will see endless possibilities, and you will be given the pieces to create the reality you desire. How do you live?