Hermes is the primary traveling companion of the protagonist, Kino, and takes the form of a talking motorcycle. Specifically, it is a type of vehicle known as a Motorrad, which is distinguished from flying motorcycles by its inability to use anti-gravity technology called lifters. Its physical design is based on a real-world classic, the British-made Brough Superior SS100, often called the Rolls-Royce of motorcycles. While it is an intelligent, sentient machine capable of complex speech, Hermes cannot move on its own and relies entirely on a rider to provide direction and balance.

The origin of Hermes is directly tied to the very beginning of Kino's journey. It was found in a broken state by the original traveler named Kino, who repaired the motorcycle during his stay in the Land of Adults. That traveler named the machine Hermes, after his previous Motorrad. The motorcycle remained silent until a critical moment when the original Kino was killed protecting a young girl. Immediately following the traveler's death, Hermes spoke for the first time, urging the girl to use it to escape, thus beginning her new life as the traveler Kino. The narrative never offers a definitive explanation for how a motorcycle can speak; it is presented as an ambiguous element of this world, leaving it to be interpreted as artificial intelligence, magic, or even the spirit of the original Kino.

Hermes has a well-defined and consistent personality that serves as a counterpoint to Kino's more reserved nature. It is often pessimistically realistic, unbiased, and prone to complaining, which can sometimes annoy its rider. Despite this, Hermes acts as a source of comic relief, frequently misquoting famous proverbs just enough to get them wrong, prompting Kino to correct it. It is also quite naive and will sometimes believe statements that are clearly meant as jokes. While it forms a deep bond with Kino, Hermes does not display traditional loyalty or care for a specific individual. Its core purpose is to provide speed and transportation; as long as a rider provides direction and fuel, Hermes fulfills its function. If Kino were to die, it would simply wait for another traveler to come along. Kino is fully aware of this mechanical purpose and fiercely protects Hermes from harm, not just out of friendship but also to ensure she can continue her journey.

In its role as the traveler's steed, Hermes is a constant presence, the only entity with whom Kino shares her innermost thoughts and feelings as they explore different countries. It has a notable relationship with Riku, a talking dog traveling with another wanderer named Shizu. The two frequently engage in spirited arguments and compete with each other, with Hermes derisively calling Riku a perverted dog. Beyond conversation, Hermes possesses remarkable abilities rooted in its nature as a machine. It has extensive knowledge of engineering and mechanics, once correctly assessing that a newly invented flying machine could achieve flight based solely on its design principles. It can also perform highly complex calculations, such as determining the target point of a ballistic missile from its trajectory equations, though it is capable of keeping such information to itself. Hermes can even produce sounds outside the range of human hearing to, for instance, chase away attacking dogs. Interestingly, despite being a machine of speed, Hermes personally dislikes being driven too fast, as it is concerned that high speeds will cause its internal components to break.