TV-Series
Description
Onyx, called Sidian in the English adaptation of Pokémon Horizons: The Series, is a recurring major antagonist in the anime. He holds a senior rank within the Explorers, the organization that serves as the main antagonistic force in the story, and he appears throughout the series as one of its admins. The Explorers operate under the leadership of Gibeon, and their central objective is to rediscover the mythical land of Laqua and claim its treasure, Laquium. In support of that mission they target the protagonist Liko because of her mysterious pendant, and Onyx takes part in these efforts as one of the group's operatives. By the time of the Rising Again arc, he is identified as a former general of the Explorers, indicating that his association with the organization eventually comes to an end.

Onyx is portrayed as stoic, serious, and taciturn. He speaks with an assertive tone among his equals but adopts formal, respectful language when addressing those above him in rank. His appearance matches his large presence: he is a heavily muscled man with dark skin, a two-tone red and black fringe, white hair at the back of his head, red eyebrows, yellow monolid eyes, and blue-gray eyeshadow, and he tends to stand with a hunched posture.

His role in the story develops beyond that of a straightforward enemy. At one point he infiltrates an academy under the alias Onigiri, taking part in the training held there. During this period he forms a temporary partnership with the trainer Ryme, and the two battle against Rika. The outcome of this battle reveals his personal principles. When his partner Garganacl is defeated while shielding Ryme's Espathra, Onyx states that he could not continue by sacrificing an ally, and when he is told that his defeat makes the gesture pointless, he replies that an ugly victory carries no meaning either. This sense of honor defines his more sympathetic qualities and sets him apart from more ruthless members of the Explorers.

Onyx battles at a high level, consistent with his senior standing in the Explorers. His main partner is Garganacl, a towering Pokémon, and he is also shown to own an Aerodactyl. His approach to battle emphasizes protecting those fighting alongside him, and his strength allows him to hold his own in high-level matches, including battles involving established trainers during his time at the academy.

His key relationships center on his position within the Explorers. He serves under the organization's leader Gibeon and works alongside its other admins and operatives. His closest bond, however, is with his partner Garganacl, and his conduct in battle shows that he places great value on loyalty and mutual protection. His temporary collaboration with Ryme demonstrates that he can work with others outside his organization when circumstances require it, and his later status as a former general suggests a turn away from the group's cause.
Cast