Imperial Thronesong is a full alternate-universe plotline — a space-opera AU set in Cosmic Year 649. In this AU, Caleb and MC are siblings by birth (not merely adoptive). MC is the Empress of the Imperial Empire; Caleb is the High Marshal of the Glory Federation. Their political relationship is adversarial: they clash over a cargo fleet seizure at Starport No. 7. Named universe locations include the warp point Velytio and a product called Nebulasia Apples. Caleb sends MC a Bitapup (a small creature or robot) named Tayby. The arc includes assassination-and-negotiation subplot branches and features a Duchess antagonist who sends her nephew to seduce MC as a political manoeuvre. The hook copy: 'What if a heart were just a little bigger than the entire universe?'