Both are epic jidaigeki Samurai movies about epic Fiercesome battles of warring States period, two of greatest Military campaign led by Ishida Mitsunari, on behalf of his Lord, Hideyoshi. Both feature conquests, exploits of Ishida Mitsunari, great brave, loyal, highly ambitious, wise strategist, war general of Hideyoshi, second great warlord to unite entire land of Japan. Sekigahara is more-or-less like sequel of a kind to Floating Castle.
Both are epic war movies about war between a strong dominant force & outnumbered defendant force despite odds............... Both battles involve winning using deception, heavy mind games, battle of wits & simple psychological tricks. Both movies feature a wise strategist, who tricks enemies right into his trap despite huge odds.