Boreas is a Guardian from the anime Tenkai Knights. He serves as one of the four Guardians of Quarton, the alien world from which the series' conflict originates. Specifically, Boreas is the Guardian of the portal that connects Quarton to Earth, which is located within Mr. White's shop and the Guardians' Sanctuary. His name and blue color scheme are derived from the Greek god of the north wind, symbolizing winter and coldness.

As a Guardian, Boreas is an ancient and wise being tasked with protecting the Tenkai Energy and guiding the legendary heroes known as the Tenkai Knights. He is the first Guardian to make contact with the human protagonists, sensing the potential in the new generation of Knights. Boreas is portrayed as a loyal and dutiful figure, willing to take significant risks for the sake of his mission. This is demonstrated when he decides to travel to Earth personally to find and guide the new Tenkai Knights, a decision that later becomes a point of discussion among the other Guardians. His strong sense of duty also leads him to act decisively in critical moments, such as when he uses a dimensional transport device to send the White Dragon Key to Quarton to keep it safe.

Boreas's primary motivation is the protection of Quarton and the defeat of the corrupted Lord Vilius. He plays a crucial role as the initiator of the story's main conflict, calling out to the human boy Guren and later allowing himself to be seen in order to guide Guren and his friend Ceylan to the antique shop where their Tenkai cores are kept. Once all four human protagonists are gathered, Boreas is the one who explains the complete history of Quarton to them, including the origins of the war and Vilius's tragic fall from grace. Throughout the series, he acts as a mentor and guide, providing the young Knights with essential information and support. In one instance, he directly participates in a battle, helping the Knights defeat Vilius.

His key relationships are with the four main human characters who become the Tenkai Knights: Guren (Bravenwolf), Ceylan (Tributon), Toxsa (Valorn), and Chooki (Lydendor), as well as with his fellow Guardians. He shares a particularly strong bond with Guren, whom he initially called out to. Boreas also has a significant relationship with the antagonist, Lord Vilius. The depth of the conflict between the Guardians and Vilius is highlighted when Boreas is captured by the villain in the episode "Vilius Returns," becoming a part of Vilius's new scheme against the Knights. This event underscores the personal stakes for Boreas and the danger he faces in his role. He is also shown to have a working relationship with Mr. White, the keeper of the shop that houses the portal.

In terms of development, Boreas's journey involves a transition from a passive guardian to a more active participant in the war. While he begins as an observer and guide, his capture by Vilius marks a turning point where he becomes a direct victim of the conflict. This event not only raises the tension for the human Knights but also shows Boreas's vulnerability. The other Guardians, Zephyrus, Eurus, and Notus, are introduced later, with Boreas being the only one known by name for a significant portion of the series. This establishes him as the primary representative of his order.

Boreas possesses several notable abilities. He is capable of flight and enhanced speed, and he can use his body to deflect incoming attacks. As a Guardian, he is a proficient marksman and a great wielder of Tenkai Energy. In his original form, he uses these skills to assist the Knights. Later in the series, after being captured, he is transformed into a corrupted version known as Dark Tempest Mode. In this state, he retains his original abilities but also gains access to a gun or sword weapon, making him an even more formidable combatant. This transformation represents a significant and dire change for the character, forcing him to become an adversary for the very heroes he once guided.