"Fighting Spirit" (気合い, Kiai) is the 55th chapter of the One-Punch Man manga series.
Metal Bat is fighting Senior Centipede and Rafflesidon. Metal Bat and the two monsters seem to be fighting on equal ground until Rafflesidon begins releasing gases causing Metal Bat to enter a drunk-like state, unable to fully control his movements. Senior Centipede takes this opportunity to injure Metal Bat. However, Metal Bat is able to eventually escape the state by damaging his head, an action that surprises the two monsters. Senior Centipede decides to go for a finishing blow, but Metal Bat detaches Senior Centipede's arm. Metal Bat then proceeds to defeat the two monsters with a single strike each.
After defeating the demon level monsters, B-Class and C-Class heroes, Pineapple and Mohawk, arrive at the scene. Metal Bat asks them to bring the Hero Association's sponsor and the sponsor's son to a hospital so that he could finally help his sister with her shopping bags. However, Elder Centipede emerges from the ground. The lower class heroes inform Metal Bat about the monster, stating that it previously wiped out a town and it is marked as a dragon level monster. Metal Bat tells the two other heroes to grab the sponsor and the sponsor's child and run, while he prepares to go all out.