Born Jiro in Kyoto, Hajime Saito endured a traumatic childhood witnessing bandits slaughter his parents. Left orphaned and vulnerable, he was rescued and adopted by a swordsman known as the first Saito Hajime. This mentor provided rigorous training in iaijutsu (quick-draw swordsmanship) and samurai etiquette, forging Jiro's foundational skills and values.

Tragedy struck again when assailants, seeking revenge against his mentor, attacked them. The first Saito Hajime sustained fatal wounds protecting Jiro, dying as they journeyed to seek help from Kondo Isami. To honor his mentor's sacrifice and legacy, Jiro adopted the name "Saito Hajime," specifically identifying himself as the "second Saito Hajime" upon joining Kondo's group in Mibu.

Saito presents a stern, abrasive exterior. He frequently uses harsh language and displays impatience towards those he perceives as weak or indecisive. This demeanor stems from his difficult past and a deep-seated obsession with strength. Despite his roughness, he exhibits calmness under pressure and a capacity to protect others when necessary. He holds distinct preferences, favoring soba noodles and chicken dishes while disliking sweet foods and activities like swimming.

His abilities center on exceptional swordsmanship, particularly his mastery of iaijutsu. His combat skills rank among the highest within the Miburo group, with his quick-draw technique a standout strength. Being left-handed contributes to his distinctive fighting style. Recognized as one of the "Three Wolves" of the Miburo, his vigilance and combat prowess solidify his role.

Within relationships, Kondo Isami serves as both his guardian and the leader who integrated him into the Miburo. Saito maintains a connection with Chirinu Nio, a peer of similar age, often collaborating on missions. His dynamic with the group reflects his complex nature—combining loyalty with his typically detached and critical attitude.