Sommer acts as secretary to GTO Bureau Chief Hiver, rarely seen apart from her, their partnership defined by seamless proximity. His German-derived name, meaning "summer," creates a deliberate contrast to Hiver’s French-rooted "winter," underscoring their symbolic duality.

He is hinted to be the reincarnation of Armbrust, a thread linking him to the series’ overarching lore, though the full scope of this connection remains unexplored. Beyond managing administrative tasks, Sommer engages in tactical maneuvers, such as deflecting scrutiny when caught in delicate scenarios alongside Hiver through poised, persuasive diplomacy.

Official sources omit deeper insights into his personal history or inner motivations, focusing instead on his unwavering allegiance to Hiver. His narrative purpose orbits her leadership, prioritizing loyalty and subtlety as the bedrock of their alliance.