Sei Nagumo is a prominent character in the manga and anime series 'Sakamoto Days.' He is a highly skilled assassin and a member of the Order, an elite group of assassins. Known for his laid-back personality and distinctive cat-like smile, Nagumo is both unpredictable and exceptionally deadly in combat. Despite his seemingly carefree demeanor, he is fiercely loyal to his companions and often plays a crucial role in the story’s major conflicts, serving as both an ally and a formidable opponent.