Tsukumojuku becomes George's best friend and the pair solves several detective cases together. After an accident in 1904 that causes him to travel through time into the 37th universe in 2012, he eventually helps both protagonists as a spirit.
Although Tsukumojuku is never drawn and his appearance is left to the interpretation of the reader, he is described as the most handsome boy in George Joestar's class. He gives off an aura that causes anyone to pay attention to him when he walks into a room or speaks. In his own novel, his parents considered abandoning him because he had a "birth defect of being too beautiful".
Despite being a young boy, Tsukumojuku speaks in a mature, well-mannered fashion. George states that he is the most intelligent yet also most bizarre boy in their class. As a child detective, Tsukumojuku lacks modesty and is desensitized to gruesome murders. He works with adult police officers to solve cases and has no qualms about keeping the dead skin of his classmate as a souvenir for solving their murder case. He holds the profession of a detective in high esteem. He always remains calm during cases and is confident that he can solve them, claiming that he has never felt pressured.
Tsukumojuku can often be cryptic, speaking about Beyond and in a metaphorical sense about himself that George and others do not understand.
In his own novel, his voice as a baby is way too beautiful that even singing and laughing causes his parents, doctor, and several nurses to faint from hearing it.
Tsukumojuku has a very good sense of smell. Despite the stench of Antonio Torres's rotting skin, Tsukumojuku can smell Lisa Lisa's shampoo from it, as she was hiding inside the skin in order to lure Antonio's killer.
Tsukumojuku has a Beyond, which guided him when he was the protagonist of his own novel. After becoming a secondary character in JORGE JOESTAR, his ability passed on to George Joestar, Jorge Joestar, and Dio Brando.
- An alternate universe version of him is the protagonist of Tsukumojuku, a previous novel written by the same author, Ōtarō Maijō. Another version of him is also a character in the JDC Series by Ryūsui Seiryōin, which the Tsukumojuku novel is based on.
- Tsukumojuku means 9, 10, 9, 10, 9 (九十九十九). Flipping the kanji for 9 (九) creates the astrological symbol for Jupiter, ♃. Jupiter is the Roman name for the Greek god Zeus, known as king of the gods. The kanji for ten, 十, is a cross, so Tsukumojuku's name has three gods (九) linked together by two crosses (十). If God is considered to be the Trinity, then God can be split into three. After his death, Tsukumojuku is with George in England, with Jorge in the Arrow Cross House, and with Dio Brando in his coffin, all at once.
- Tsukumojuku possibly resembles Jesus, based on the appearance of Dio's Beyond. In the Sixth Story of his own novel, Tsukumojuku encounters several of his own disembodied heads. They all have long hair and are wrapped around three times with rope to look like crowns.