Zalpha Opal, usually referred to simply as Opal, is a main character in the anime World War Blue and one of its central heroines. She is an archer serving in the special forces of the Segua Kingdom, a nation engaged in a prolonged war with the rival Ninteldo Empire. Her character is inspired by Opa-Opa from the Fantasy Zone video game series. In appearance, she is a young woman standing about 168 centimeters tall, with purple hair and violet eyes.

Opal is introduced as a proud and capable soldier who is wary of newcomers. When the fast and confident young warrior Gear is added to the special forces without her approval, she confronts him and challenges him to a duel to test whether he has the right to remain in the unit. Gear defeats her instantly, but instead of holding a grudge, Opal is impressed. After Gear explains that he admires people who strive to move forward, she acknowledges his strength and treats him with respect. This exchange shapes her personality as someone who values skill, sincerity, and forward-looking determination over pride.

Her motivation centers on loyalty to Segua and the successful completion of her military duties. As part of the special forces, she is assigned the mission of rescuing General Alex, the kingdom's strongest warrior, from the Ninteldo-allied country of Tatrand. Within the story, Opal serves as both a frontline combatant and the main heroine of the unit, working alongside Gear, the mercenary Tejirov, and the vice-general Ramses, who assembles the team. Her most significant relationship is with Gear, which develops from initial distrust and rivalry into mutual respect and a close working bond.

Her character development across the story is tied to this shift in attitude, as her early suspicion of Gear gives way to acceptance of him as a worthy comrade. Her notable ability is her archery, which defines her role in the special forces and provides the team with a skilled ranged combatant in their operations.