"Grenadier" is a 12-episode anime series set in a fictional world resembling feudal Japan, blending elements of action, comedy, and drama. The story centers on Yajiro Kojima, a skilled samurai who becomes disillusioned with violence after witnessing the horrors of war. While wandering, he encounters Tenshi, a cheerful and highly skilled gunfighter known as the "Smiling Senshi." Tenshi wields a unique revolver and possesses extraordinary marksmanship, using her abilities to protect the innocent and uphold peace.

Tenshi is on a mission to recover her stolen weapons, which were taken by a rogue military faction seeking to destabilize the region. Yajiro, initially reluctant to engage in further conflict, is drawn into Tenshi's quest after witnessing her unwavering resolve and kindness. Together, they travel across the land, facing various adversaries and uncovering a larger conspiracy involving corrupt officials and a shadowy organization manipulating events for their own gain.

The narrative explores themes of redemption, the consequences of violence, and the pursuit of peace. Tenshi's optimistic and pacifistic approach contrasts with Yajiro's more cynical worldview, creating a dynamic partnership that evolves throughout the series. Supporting characters, such as the resourceful thief Mikan and the stoic warrior Rushuna, add depth to the story, each contributing to the overarching plot in meaningful ways.

As the duo progresses, they confront increasingly powerful enemies, culminating in a climactic battle that tests their resolve and ideals. The series balances action-packed sequences with moments of introspection, highlighting the characters' growth and the moral complexities of their journey. "Grenadier" concludes with a resolution that underscores the importance of hope and perseverance in the face of adversity, leaving a lasting impression on its audience.