The first one that always leaps to mind is Lian Hearn's 'Tales of the Otori'. It's a sprawling fantasy epic, but the heart of it is the brutal struggle for power between the Otori, Tohan, and Seishuu clans. The political maneuvering is constant—marriage alliances, espionage, betrayals that reverbate for generations. It's less about the big battles and more about the quiet, deadly game of influence played in audience chambers and tea houses.
If you want something grounded more strictly in history, I can't recommend 'Shogun' by James Clavell enough. It's monumental. The rivalry between Toranaga and Ishido is a masterclass in tension, where every conversation is a duel and every gesture holds political weight. The way it explores the conflict between different clan loyalties, bushido, and pragmatism is absolutely gripping.
For a slightly different angle, 'The Samurai's Garden' by Gail Tsukiyama touches on these themes through a more personal, familial lens, set against the backdrop of rising nationalism. The clan dynamics are internal, within a household, but it echoes the larger societal shifts of the era. It’s a quieter, more atmospheric read that still captures that sense of duty and simmering conflict.