Keiichi Morisato is the central human protagonist of the story. He is introduced as a college student at the Nekomi Institute of Technology, where he is also a dedicated member of the university's Motor Club. His background reveals that he originally comes from the Kushiro subprefecture in northeastern Hokkaidō, the northern island of Japan. His family includes his father Keima, a glassblower with a natural talent for motorcycle maintenance, his mother Takano, and his younger sister Megumi.

Physically, Keiichi is noted for his short stature, but this is contrasted by a strong and reliable character. His personality is defined by a fundamental kindness and a desire not to see others hurt. This pure and innocent nature is a core aspect of his being, though it sometimes makes it difficult for him to openly express his deeper feelings, particularly his love for Belldandy. Despite occasional shyness or indecisiveness, Keiichi is not unintelligent; he can be quite sharp and will speak his mind when a situation genuinely calls for it, demonstrating a level-headedness that often makes him the voice of reason among the extraordinary beings he lives with.

His motivations are deeply rooted in his relationships. The story begins when he accidentally dials the Goddess Relief Office and, believing the resulting appearance of the goddess Belldandy to be a prank by his seniors, wishes for a girl like her to stay by his side forever. This wish is granted, and his primary motivation throughout the series becomes maintaining this bond and supporting Belldandy, even as they face challenges from both the mortal and divine realms. He is shown to be incredibly reliable when it comes to matters of love and commitment.

Keiichi plays the pivotal role of the mortal anchor in a household that soon includes Belldandy and her sisters, Urd and Skuld. He is not a hero in the traditional action sense; rather, his role is to provide a human perspective and a source of steadfast kindness that influences the goddesses and other supernatural beings he encounters. His key relationships include his deep, loving bond with Belldandy, which is the emotional core of the series. He also acts as a caring, if sometimes exasperated, housemate to the mischievous Urd and the brilliant but temperamental Skuld.

Throughout the narrative, Keiichi undergoes significant development. While always a good person, he grows more confident and his skills become more pronounced. A major turning point in the manga reveals that a powerful seal was placed on him by Heaven when he first made his contract with Belldandy, suppressing his desires and longings to maintain the separation between gods and men. This revelation adds a complex layer to his previously perceived innocence, and his journey to overcome this external limitation marks a crucial step in his personal growth and the maturation of his relationship with Belldandy.

Keiichi possesses several notable abilities that distinguish him. He is an exceptionally skilled mechanic and an outstanding race car driver, talents that are central to his character and often play a key role in the story. His abilities with machines are so profound that he is recognized by the mechanical race known as the Machiners as someone who understands how machines feel. His pure-hearted nature also grants him unique supernatural aptitudes. He has been able to temporarily host angels, including Lind's angel Cool Mint and the angel-demon hybrid Blue Lance, a feat that is extraordinary for a human and is attributed to the love and trust he receives from the goddesses around him.