In its upright position, the King of Cups symbolizes diplomacy, compassion, and being emotionally balanced. He sits on a large stone throne and seems to be looking away from the cup, which suggests that he's mastered his emotions and doesn't need to focus that much on his emotionality.
In reverse, the King of Cups represents inner feelings, being emotionally manipulative, and moodiness.
How does this tie in to Joel? Like the King of Cups in reverse, Joel was (and still is, to some degree), at his core, a sensitive and moody individual focused on his inner feelings. He started as a very sensitive and emotional young boy, but he later learns to distance himself from his emotions.
Eventually, he becomes an argumentative, stubborn teen and young man who refuses to show his emotions and barricades others, including his beloved Malka, from understanding who he really is. However, he is still letting his emotions control him, since if he had truly mastered his emotions, there would be no need for self-denial and self-flagellation.
Once he accepts his own desire to give and receive love, he gains better control over his emotional self. He learns to love Malka, put others before himself (which was hard to do when he was still so egotistic), and value compassion over proving a point.
I chose to represent Joel as a merman because the King of Cups is associated with the water. According to my research, the King of Cups is the fire aspect of water, which means he represents the intuitive and emotional aspect of water. The King of Cups has also been compared to a seasoned mariner who can drive a ship safely through storms. Joel, similarly, can navigate upheavals in his personal life calmly, due to how he was raised and how he’s steeled his nerves over the years.