He seems to be one of the kinder or more considerate brothers, as he showed concern for Turtle when told about Anemone's soul. He seemed cautious of animus magic, and appears to have a sense of humor, such as when he joked about bringing all his brothers with him on the mapping mission. He appears to be intelligent, and he may have an interest in mapmaking.
The Dragonet Prophecy
Fin was indirectly mentioned when Anemone says she has brothers she can't play with because they are too rough.
The Jade Mountain Prophecy
Fin was mentioned indirectly when Turtle told Tsunami that she had thirty-two brothers.
Fin was seen when Turtle is going to warn his mother about Anemone. Fin sees Turtle and wonders why he has left Jade Mountain Academy to return to the Deep Palace. He refers to the academy as a "fancy hugging school." Turtle then tells him to gather their brothers and take them all away from the palace, which Fin takes seriously. Fin says that he may as well go on that "mapping expedition" he was planning to do, and would see if he could bring all of his brothers with him for their safekeeping. He jokes that taking all of his brothers away from the palace will be more like an invasion than a mapping expedition.
Coral indirectly mentions Fin in the letter she sent to Turtle in the epilogue, saying how Turtle's brothers believed that he played a prank on them the last time he was at the palace and warns him to check his bed for lobsters the next time he visits, indicating that they will try to get back at him.
Present: Abalone • Flounder • Herring • Kelp • Lagoon • Nautilus • Pearl • Piranha • Riptide • Snail • Snapper • Squid • Tempest • Tortoise • Urchin • Webs • Whirlpool