Julius Rainburg is a prominent character in the anime Wistoria: Wand and Sword, known for his exceptional magical talent and his role as a rival to the protagonist, Will Serfort. As a top student at the Regarden Magical Academy, he is a sixteen-year-old mage who specializes in powerful ice magic. Physically, Julius has a distinctive appearance with medium-length, wavy cyan hair and matching cyan eyes, often seen wearing a light-colored long-sleeved shirt, dark pants, his student robe, and a notable rose-shaped ornament made of real ice.

In terms of personality, Julius is initially presented as an arrogant and prideful noble who looks down on those he considers inferior. He holds an immense dislike for Will Serfort, scorning him for his inability to use magic, and is openly racist towards dwarves, once cruelly telling them to leave the country. However, his character is not without depth; a past heartbreak involving his family's maid, Anna, who praised his kindness only to marry another man, hardened his heart and led him to swear off his former, gentler self. Despite his cold exterior, he is self-aware enough to recognize that he is a leftover for still being at the academy and is driven by a desperate need to become stronger.

Julius's primary motivation is his ambition to become the successor to Elfaria Albis Serfort, one of the most powerful mages in the world and a legendary figure in ice magic. His desire to reach her level is what fuels his actions and his intense rivalry with Will. His role in the story is largely defined by this rivalry, which comes to a head during the Grand Magic Festival. After he belittles the dwarven workers at a tavern where Will is employed, a confrontation ensues that leads Julius to challenge Will to a duel during the festival, threatening to have him expelled if he loses. In their subsequent battle, Julius unveils his signature spell, Ars Weiss, one of the twelve secret ice magics created by Elfaria, which allows him to create numerous ice clones of himself. Despite his confidence in this power, Will is able to defeat him by exploiting the spell's imperfections, revealing that Julius requires the assistance of his teammates to control the clones properly and that the ice crystals forming around their feet give away the real Julius. Will also humbles Julius by informing him that Elfaria invented the spell when she was merely two years old, shattering his illusions of grandeur. Following his loss, Julius is forced to honor his bet by working as a dishwasher in the dwarves' bar as an act of apology, marking a significant turning point for his character.

Key relationships for Julius include his childhood friend Emma Klever, with whom he shares a history that later becomes tied to a tragic fate. He also has a rivalry with his classmate Sion Ulster, a fire magic user. Over time, his dynamic with Will Serfort evolves from pure antagonism to a more complex professional relationship, where despite his harsh words, he is able to cooperate with Will when necessary, such as during comprehensive training. As a mage, Julius's notable abilities are formidable, ranking him third in his class. He is skilled in low to mid-tier ice magic spells like Zelnea Caulis, which creates a large mass of ice to drop on a target, and can use common magic like Search to detect others. His ultimate technique is his incomplete version of Ars Weiss, though he later develops an incredibly powerful spell called Armenta Auliscas, which generates a massive ice barrage but requires a long incantation. In a significant turn of events in his development, Julius is later chosen for an undercover mission by the Ice Faction, during which he discovers something strange about his friend Emma and is ultimately killed by an entity named Shade, leaving behind a lingering mystery.