Shinpei Gotou

Age: 18

A hired assassin ordered to kill Satoko, who was captured by unknown men. He was tasked with her death but is persuaded to marry her to aid her, though his intense love repeatedly causes trouble for Satoko.

Goto exhibits significant mental instability, showcasing a chilling ease in taking lives without a hint of remorse or guilt. He doesn't hesitate to kill and appears to derive pleasure from it, even laughing after ending multiple lives. Initially, despite a fleeting act of kindness towards Satoko by offering her some rice, he lacks empathy towards her, willing to spare her life only if the reward for doing so exceeds what he would gain by killing her.

After Satoko displayed what Goto stated as a tolerance for him he fell head over heels in love with her.

His demeanor is characterized by a teasing and somewhat callous nature, although he occasionally displays a more caring and protective side, particularly towards Satoko and those he values. This protective instinct reveals a different facet of his personality beneath the otherwise unstable and ruthless exterior.

(Source: Firefly Wedding Wiki)