In metaphor, "sea" represents a vast and boundless world, which implies that a person's inner world is full of infinite possibilities and vastness. At the same time, the "sea" also symbolizes the infinite expansion and enrichment of one's emotions, thoughts and imagination, just like the ocean.
Therefore, "Na Pianhai in My Heart" expresses the vastness, profundity and beauty of one's inner world, and also represents one's yearning and pursuit for the future, implying that they will make constant efforts to pursue their own ideals and goals.