Taro Sakamoto is the protagonist of the manga Sakamoto Days. Once a legendary hitman, he now leads a peaceful daily life running a small grocery store with his family. While he usually looks like a chubby middle-aged shopkeeper, he unleashes his prime-era combat skills and mastery of using everyday objects as weapons whenever his family or daily life is threatened. Identity and Background Sakamoto is introduced as a figure whom all hitmen admired and all villains feared. He quit the hitman life after falling in love with Aoi, who worked at a convenience store. He eventually married her, had a daughter, and now runs a private shop in a quiet town. Currently known as the manager of Sakamoto Store, he is depicted as a man striving to protect the peace of his family and daily life. At the same time, he remains the central axis between the mundane and the extraordinary as he becomes entangled with the Japan Association of Hitmen (JAA), its elite special task force ORDER, and the mysterious figure X (Slur).

The Sakamoto family consists of the father Taro Sakamoto, the mother Aoi Sakamoto, and the daughter Hana Sakamoto. Since the core premise of the work is Sakamoto facing threats from assassins to protect his family and peaceful life, Aoi and Hana serve as the devices that explain Sakamoto's principles of action. In particular, Sakamoto's rule of "not killing people" while fighting is closely linked to his everyday goal of protecting his family. Aoi is the mother of the Sakamoto family and is introduced as a clerk at Sakamoto Store. Although Taro Sakamoto was a legendary former hitman, he moved to a life of running a private shop in a quiet town after marrying Aoi and starting a family.

Lu Shaotang is a Chinese martial artist in the manga Sakamoto Days. She is the daughter of a Chinese mafia boss, but after losing her parents, she was pursued by the Tan Syndicate for the key to the family safe until she received help from Sakamoto and Shin. She later joins Sakamoto Store as the clerk in charge of meat buns to become independent. She travels together with the rest of the Sakamoto Store family.

Shin Asakura is the sub-protagonist of the manga Sakamoto Days. He is a telepath who can read minds and is the partner of former hitman Taro Sakamoto. Initially, he approached Sakamoto to persuade him to return to the underworld, but he eventually became a colleague at Sakamoto Store, fighting alongside him to protect their family and daily life. He is characterized by his blonde hair parted down the middle and his relatively small build. Shin and Sakamoto's Partnership The Importance of Telepathic Communication Shin's ability is not just a combat aid; it functions to convey the intentions of the nearly silent Sakamoto to the readers and surrounding characters. Even when Sakamoto remains silent, Shin reads his thoughts or the situation and reacts, leading to chemistry that is both comical and strategic. The fun of this relationship lies in Shin's transformation from an "outsider who came to persuade" to a "colleague who shares the same will." Because he was inspired by seeing Sakamoto fight to protect his family and daily life, their bond is closer to a shared belief than a contractual relationship. Role as a Growing Partner Shin is defined as a "growing partner" in official introductions. While he initially plays a large role in reading situations and assisting Sakamoto from the sidelines, he continues to develop his own strength.

Heisuke Mashimo is a character in Sakamoto Days, a sniper connected to Sakamoto Store whose clumsy personality contrasts with his outstanding marksmanship. In the live-action film, he is portrayed by Junki Totsuka. He is mentioned as a character who helps Sakamoto alongside his best friend, a yellow bird named Piisuke. While Heisuke gives off an air of being a bit scatterbrained on the surface, he is depicted as a man with definitive sniping skills in actual combat. There is also a setting where he begs for food at Sakamoto Store because he is short on money, making his relatable and comical character traits stand out more than a powerful hitman image. Piisuke is introduced as a yellow bird that always travels with Heisuke. He is also linked to an episode where he participates in a survival game hosted by the shopping district aiming for a 1 million yen prize.

Hana Sakamoto is the daughter of Taro Sakamoto in Sakamoto Days. Since the story follows former hitman Sakamoto protecting his home and daily life after retirement, Hana is a character placed at the core of the family axis, serving as his primary motivation to keep fighting.