Elmo is an artificial human created through alchemy by Jolly, a prominent member of the Arcana Famiglia. He was designed as a homunculus, and among many attempted creations, he was the first to succeed in forming a contract with a Tarocco, marking him as a distinct and successful experiment. His physical appearance is that of a young boy with black hair and eyes that are described as either red or dark orange. He is typically dressed in an orange jacket, a brown vest with a red kerchief over his shoulders, and brown shorts held up by suspenders, paired with brown boots.

His personality is calm, quiet, and reserved, with a notable curiosity about living things and the world around him. Elmo enjoys reading books, particularly those belonging to Jolly, though he finds texts related to alchemy difficult to understand. While he is content to study, he experiences the most joy when he is allowed to go outside, interact with new people, and explore the world, behaving in many ways like a real child despite his artificial origins. He struggles to express himself clearly, which can make it difficult for others to understand his feelings.

Elmo is deeply motivated by a desire to be useful to his creator, Jolly, whom he views as a father figure. He trusts Jolly completely and is scared of disappointing him, leading him to obey everything his creator says. His role within the story is initially that of a mysterious child who appears during the Piccolino festival on the island of Regalo. Unlike the other children, he stays behind after the festival to ask Felicità for advice, confessing that he feels an unfamiliar pain in his chest, which leads the other characters to conclude he has developed feelings for her. In the sequel, he becomes one of Felicità's potential love interests.

His most significant relationship is with Jolly, his creator and surrogate father, who, despite a general dislike for children, shows care for Elmo. Elmo is also deeply attached to Felicità, taking a liking to her immediately and wishing to spend time with her. When Felicità loses her memories after using the power of the Wheel of Fortune, Elmo is visibly saddened that she no longer remembers him and begs Jolly to help her, demonstrating his strong emotional bond with her. Jolly's normally cold and reserved character is shown to soften when interacting with Elmo, as he is patient and caring toward the boy, which surprises Felicità.

Elmo undergoes development primarily through his interactions with Felicità. His struggle to understand his own emotions, particularly the pain of falling in love, leads him to fear that he might be dying, forcing Jolly to explain that love is not fatal. After Felicità loses her memories, his insistence on finding a way to help her, even when Jolly claims it is impossible, inspires Jolly to develop a new solution, showing Elmo's growing emotional maturity and independence.

Elmo possesses a unique and notable ability derived from his contract with the Sixteenth Tarocco, the Tower. This power allows him to generate protective force fields around a specified area. The stigmata associated with this Arcana is located on his right hip. At first, his power is only strong enough to protect Jolly's laboratory, but Jolly hopes that as Elmo grows, his power will increase sufficiently to cover the entire island of Regalo, thereby easing the burden on the family's leader, Mondo. His physical growth is also notably rapid, and he continues to absorb knowledge from the books Jolly provides.