Puck, also referred to as Robin Goodfellow, is a small fairy-like creature with wings who serves as a recurring companion and ally within the story. His origins lie with the alien collective known as the Kiltgang, the primary opposing force in the series, but he breaks away from them early on and chooses to side with the human defenders of Earth. Because of this, much of his background remains wrapped in mystery for a long stretch of the narrative, and his true reasons for switching sides are not immediately made clear.

In terms of personality, Puck is mischievous and playful, with a decidedly teasing streak. He frequently hovers around the main characters, provoking them with sarcastic remarks and enjoying pranks and tricks. His sense of humor is childlike and he speaks in a light, playful tone, which makes him seem harmless at first. Beneath this playful exterior, however, he is a powerful and enigmatic being. He is curious and analytical, enjoys tackling problems and new challenges, and demonstrates a quick wit that makes him a useful presence in difficult situations. Despite his constant joking, he shows a strong sense of loyalty toward those he considers friends and is willing to go to considerable lengths to protect them.

His motivations are one of the character's defining mysteries. For much of the series, his genuine intentions remain ambiguous, and it is unclear whether his allegiance to the human side is sincere or part of a larger agenda. As the story progresses, his past and true purposes are gradually revealed, and he develops into a significantly more important figure in the ongoing struggle against the Kiltgang.

In battle and in daily interaction alike, Puck acts as a valuable asset to the pilot Daichi Manatsu and the people around him. His most notable ability is the power to control gravity, allowing him to generate powerful gravitational fields that can immobilize enemies or draw objects toward him. He also possesses the ability to take on a humanoid form and can manipulate reality to a degree, creating illusions, teleporting, and shapeshifting at will. In addition, he is able to merge with machines, which lets him take control of them and use them for his own purposes. These abilities make him an important resource in combat against the Kiltgang and their robotic monstrosities, and his unique powers combined with his quirky temperament make him a memorable presence throughout the series.