Wonderweiss Margera is an arrancar in Sōsuke Aizen's army, though not part of the Espada. His spiritual power is ranked on par with the Espada by Soul Society. Wonderweiss has a small, thin build and appears somewhat child-like. The remnants of his hollow mask sit atop his head, resembling a tiara or small crown. His personality is also child-like and even autistic. When tasked with a mission to kill, he instead plays with a dragonfly. He shows brief hostility, firing a retaliatory bala blast, but quickly returns to his usual demeanor. He can only speak in simple syllables, much like a child.
Kaname Tōsen notes that Wonderweiss, like himself, is a pure being, though it's unclear whether this purity is good or evil. This purity often leads pure beings to stick together, which explains why Wonderweiss follows Tōsen everywhere when possible. He even tried to restrain Gin Ichimaru from getting close to Tōsen, as he was wary of him.
Wonderweiss's zanpakutō is a large purple sword strapped to his back, about as tall as he is. Its hilt resembles a western longsword rather than a katana, although it retains the familiar hilt weaving. The guard looks like an Egyptian eye. The name and released state of his zanpakutō have not been revealed.
In the "Fake Karakura Town" arc, it is revealed that Wonderweiss is a "modified arrancar," specifically created to seal Ryuujin Jakka's flames. Aizen considered Head Captain Yamamoto to be the greatest threat to his plans, so he created Wonderweiss by sacrificing all of the arrancar's emotions, memories, and ability to speak.
