Kai-no-kami Nagamasa Kuroda is a Christian daimyo, eldest son and successor to strategist Kanbei Kuroda. Historically involved in the Battle of Sekigahara, he became one of the most rewarded vassals following the conflict. He stands 188 cm tall and is 28 years old during depicted events. His personal interests encompass maintaining war supplies like weaponry and armor, alongside a preference for eating squid.

Nagamasa presents as a lean, spiteful perfectionist consumed by the desire to earn his father's approval. After Kanbei instructs him to align with Tokugawa Ieyasu, Nagamasa pursues ultimate victory. This drive leads him to participate in an assassination attempt against Ishida Mitsunari in Kyoto. The effort fails when Sakon Shima deflects his blade, enabling Mitsunari's escape.

During the conflict, Nagamasa supports Hosokawa Tadaoki's initial charge against the Western Army. His forces suffer defeat due to Sakon's cavalry tactics. Identifying Sakon as a critical threat, Nagamasa retreats to a distant thicket and commands his riflemen to concentrate fire on him. One shot strikes Sakon's left shoulder, inflicting a wound that ultimately proves fatal. Nagamasa habitually uses the phrase "No good" (イカン, ikan), a trait prompting Ukita to mock him with the pun "Squid" (イカ, ika). His actions stem from loyalty to the Tokugawa cause and personal ambition to secure recognition and success.