Densuke is a dog-shaped petmaton, a type of virtual pet, who belongs to the main protagonist Yuko Okonogi, known as Yasako. He is a gift to Yasako from her grandfather, a doctor who was involved in cybernetic medicine, and he serves as a cherished memento of him. In appearance, Densuke is not designed to be a traditionally cute or flashy creature; his design is more clumsy and imperfect, yet this makes him endearing to those who come to know his loyal heart. Despite being a computer-generated entity only visible through the special cyber-glasses that children use to interact with the augmented reality world, Densuke is treated as a full member of the family, possessing a distinct personality and a profound emotional connection with his owners.

Densuke's most defining trait is his unwavering bravery and deep loyalty, particularly towards Yasako and her younger sister Kyoko. While his appearance and mannerisms often reflect the simple, energetic playfulness of a real dog, he consistently demonstrates a serious and protective nature when his family is in danger. He is a creature of action rather than words, expressing his devotion through his deeds. Even when he is badly injured, he shows remarkable courage, such as when he fights off a group of Nulls to protect Yasako or when he risks himself to carry Kyoko's captured computer body to safety, performing the role of a heroic guardian that his real-world form cannot always fulfill. This steadfast nature makes him a deeply trusted companion, and he is often looked to for support in the most perilous situations. He functions as a comforting, inspirational presence for the children, embodying a pure and selfless love.

Throughout the story, Densuke is far more than just a pet. He is an integral part of the narrative and the key to unlocking many of its central mysteries. As the plot progresses, it is revealed that Densuke is not an ordinary virtual pet. He is referred to as a Coils life, a kind of genuine artificial life that is fundamentally different from standard simulated pets, and he is believed to hold the key to accessing the mysterious Coil domain. This ability makes him a target for various characters and organizations who seek to enter that realm. For instance, the government agent Nekome tries to use Densuke to open a stable portal, and he is later identified as a crucial element that can manipulate the very fabric of the otherworldly Coil space. In a particularly poignant moment, Yasako is able to reach into the Coil space and hold Densuke, remarking that his body is warm, which highlights the blurred line between the digital and the real and underscores the deep bond they share.

Densuke's primary relationship is with Yasako, his owner, to whom he is utterly devoted. He is also very close to Kyoko, who shares a more playful, childlike dynamic with him, often imitating her sister's actions with him in a fun and energetic way. His interactions with the other children, such as the hacker Isako and the members of the Cyber Detective Agency, are typically defined by the situation's urgency, with them relying on his unique abilities to help them overcome obstacles in the virtual world. Over the course of the series, the emotional significance of Densuke deepens considerably. His presence forces the characters, especially Yasako and her mother, to confront difficult themes of loss and the process of moving forward. The story does not shy away from the pain that comes with loving a pet, even a virtual one, as Densuke's fate becomes tied to the resolution of the central conflict. In the end, his journey is not about grand power, but about the gentle strength and comfort he provides, and the lesson that even when a beloved companion must leave, the love shared remains a guiding force toward the future. Among his notable abilities, Densuke has shown he can carry computer bodies, navigate unstable digital spaces, and his very existence is central to opening portals into the deepest layers of the city's hidden cyber-network.