The Mongol Empire's collapse wasn't just a matter of khans and kurultai — it was also the work of an obscure prince who set the stage for the Toluid Civil War. In this episode, Lucas and Luna pick up after the death of Möngke Khan and examine the forgotten figure of Arpa Keun, a great-grandson of Chagatai who briefly seized power in the chaos following Möngke's death. Arpa's short-lived reign — just a few months in 1259-1260 — exposed the deep fractures in the Mongol world, as he attempted to reform the Yassa and curry favor with the Jochid faction, only to be deposed by a coalition of princes loyal to the Toluid line. Through Arpa's story, we see how the empire's unity was already a fragile idea, contested not just by Khubilai and Ariq Böke, but by lesser princes who saw opportunity in the vacuum. Lucas traces Arpa's rise from obscurity to the throne at Karakorum, his doomed alliance with Berke Khan, and his ultimate execution near the Onon River. Along the way, we revisit the shifting loyalties of the Chagatai Khanate, the role of the Yassa in legitimizing rule, and the quiet ways that the empire's infrastructure — the yam riders, the paizi, the ortoq merchants — kept working even as the political center collapsed. It's a story of a man almost erased from history, but whose brief moment in the sun reveals how quickly the Mongol dream fractured.