Adam is a young British musician who serves as a central figure in the story. He is approximately twenty years old, with blond hair and blue eyes, and his presence carries an air of mystery from the moment he is introduced. As the lead singer of a band called Evil Eye, his music is a defining aspect of his character, possessing a captivating quality that draws people to him.

Adam's background is rooted in tragedy. Before the events of the story, he was in a deep relationship with a young pianist named Sayaka Kamijo. Their time together was cut short when Sayaka died at the age of seventeen due to an illness. Unable to cope with this devastating loss, Adam is implied to have taken his own life at the age of twenty, with some sources suggesting he struggled with drug addiction following her death. His physical death occurs in 1979, years before he encounters the protagonist Mizuki Mochizuki.

Following his death, Adam exists as a wandering spirit, endlessly searching for his lost love Sayaka. His personality is defined by this lingering grief and a profound sense of longing. He is a melancholic figure, frequently playing a sad, haunting melody on his guitar which is later revealed to be the song titled Last Quarter. This sorrow often manifests as a confusion between the past and the present. When he meets Mizuki, he is initially drawn to her because she resembles Sayaka, and he sometimes sees her only as a replacement for his deceased girlfriend, pleading with her not to die.

Despite this, Adam forms a crucial bond with Mizuki. After meeting her one night in Shibuya while playing his guitar, he invites her to live with him in an abandoned mansion. Over the course of two weeks, a genuine connection forms, and he plays her favorite song, Last Quarter, to comfort her during moments of sadness. Adam's role in the story is that of a catalyst and a tragic romantic interest. He is the reason Mizuki runs away from her unhappy home life, an act that leads directly to her near-fatal car accident. While she lies in a coma, her soul, having lost her memories, becomes trapped in the same mansion, remembering only the name Adam.

The central mystery of the plot involves the children who find Mizuki's spirit and, knowing her only as Eve, seek to reunite her with Adam. Through their investigation, they uncover the truth of Adam's death and his history with Sayaka. The most significant aspect of Adam's development is the evolution of his feelings. Initially, his interest in Mizuki is purely because she is a reflection of his lost love. However, during the lunar cycle in which her soul wanders, he spends time with her and genuinely falls in love with Mizuki for who she is. This creates a complex dynamic where he is both trying to reunite with Sayaka's spirit, which has possessed Mizuki, while also developing a new love for the living girl.

In the end, Adam's role is to provide closure. He leads the spirit of Sayaka out of Mizuki, allowing the young woman to wake from her coma, though she retains no memory of him or the time they spent together. As a spirit, Adam has the notable ability to exist in a liminal space between life and death, and his music serves as a powerful, almost supernatural force. His song Last Quarter acts as a beacon, calling out to Sayaka and ultimately leading her spirit to possess Mizuki. While he possesses no overt physical powers, his presence and his art are potent enough to bridge the worlds of the living and the dead, influencing the fates of everyone he encounters.