Sakamoto Days follows Tarou Sakamoto, a legendary hitman whose name once inspired fear in every villain and earned the respect of fellow assassins. At the height of his career, Sakamoto seemed untouchable, but everything changes when he falls in love. In just five short years, he marries, becomes a father, gains weight, and leaves behind his weapons to run a modest convenience store, choosing a quiet family life over the violence that made him famous.
Retirement, however, does not mean the underworld has forgotten him. Sakamoto struggles to keep his past buried when Shin Asakura, his former partner, returns and decides to stay with his family under their strict no-kill rule. Soon after, a huge bounty is placed on Sakamoto's head, and assassin after assassin begins closing in on the supposedly retired legend. What they find is that Sakamoto has not lost his instincts or his skill. Even while protecting the family he loves, he can still outfight, outthink, and outlast anyone who comes after him, turning every attack into another reminder that the most dangerous man in the room is the one who wants only a peaceful life.