Based strictly on the provided description, Matheus Johann Weiss is Vice Commander and 2nd Company Commander of the Imperial 203rd Aerial Mage Battalion, initially appointed by Tanya von Degurechaff after his transfer from the Eastern Army. His rank advanced from First Lieutenant to Captain and then Major during operations. He possesses a curved face, black hair, and black eyes, though an alternative description notes violet eyes, consistently wearing standard Imperial military battle suits for combat and officer uniforms otherwise. Weiss demonstrates a prudent yet competent personality, effectively managing and disciplining subordinates while showing consistent concern for their welfare, earning their confidence. Initially employing strictly textbook combat tactics, he developed more aggressive approaches during conflicts, periodically impressing Tanya. His relationship with her combines loyalty with apprehension; he experiences shock at some of her statements yet remains a trusted subordinate delegated significant responsibilities. He maintains positive rapport with fellow officers like Grantz and Serebryakov, showing particular consideration for the latter as one of the battalion's few female members. Within the Isekai Quartet crossover scenario, he appears among characters transported to a parallel world. During the film *Another World*, he fought rogue golems alongside Tanya, Raphtalia, and others after being separated by a wormhole. Following the 203rd Battalion's expansion into Kampfgruppe Salamander, Weiss retained the Vice Commander position under Tanya, assuming full battalion command during her absences. His additional duties involved coordinating between different battalions within the regiment, a role that initially caused friction with an infantry major before unit replacements resolved tensions.