Mackey Stingray is introduced as the younger brother of Sylia Stingray, the leader of the Knight Sabers, but a significant revelation alters his place in the story. He is actually one of the earliest prototypes of the boomer androids created by his father, Professor Katsuhito Stingray, in the Wiz Lab. Because he is a human-like boomer who was built as a prototype, he was considered a failure for being too organic and was later classified as a possible younger sibling. This truth is kept hidden for much of the series, and Mackey himself is unaware of his own true nature.

Mackey is a naive, curious, and awkward character with a deep passion for computers, machines, and technology. He is naturally shy and often ends up in situations that make him seem perverted, such as accidentally walking in on the Knight Sabers while they are changing, though this is unintentional and a source of embarrassment for him. He is very sweet, easygoing, and does not behave like a machine at all. He has a genuine love for repairing and maintaining machines, believing that machines know if they have been put together correctly. This passion earns the respect and attention of the stern mechanic Nigel Kirkland, whose apprentice he becomes.

Mackey's primary motivation is to support his sister Sylia and the Knight Sabers. He cares deeply for Sylia and serves as one of the few emotional anchors in her life, often being the one who keeps her from spiraling out of control. He does not seek fame or glory but finds fulfillment in using his technical skills to help the team. His relationship with Nene Romanova is also a driving force for him, as he develops sincere romantic feelings for her despite the early misunderstandings that make her initially suspicious of him.

In the story, Mackey serves as the Knight Sabers' youthful mascot, mechanic, and support driver. He is responsible for maintaining Priss Asagiri's motorcycle, which requires constant repairs due to her aggressive driving, and he is the sole caretaker of the hardsuits the team uses in battle. He can pilot an armored suit himself when a mission calls for it and drives a large transport truck that delivers the Knight Sabers and their bikes to the scene of a conflict. Alongside Nigel Kirkland, he helps build and repair the team's equipment, including the second-generation suits made from a liquid biometal after their original suits are destroyed.

Mackey undergoes significant development throughout the series. His connection to the super-boomer Galatea, who is also a creation of his father, is a central part of his arc. Because of this link, Galatea is able to manipulate him, and she eventually wipes his memories clean, regarding them as false data. This loss includes all of his feelings for Nene, causing great pain to those who care about him. His sacrifice of his remaining consciousness grants the Knight Sabers a vital opening to enter Galatea's tower for their final confrontation. After Galatea is destroyed at the conclusion of the series, Mackey's memories and sense of self are restored, leading to a reconciliation with Sylia and Nigel.

Notable abilities include his prodigious skill with computers and technology, which makes him an exceptional hacker and mechanic. He is capable of repairing, modifying, and even building advanced machinery, including the Knight Sabers' hardsuits. He can also pilot an armored suit himself when necessary. His driving of the team's transport vehicle is another practical but critical skill. On a more personal level, his true nature as a boomer prototype gives him a unique connection to Galatea, which is both a vulnerability and a key plot point in the series.