SL-Man operates as a sentient steam locomotive within the Anpanman universe, primarily providing rail transportation for goods and children. His movement includes distinctive arm motions whether running on or off rails. Discovered rusted and inoperative during a severe storm, he was struck by lightning that toppled a tree onto him, rendering him unconscious. Baikinman then found and kidnapped him, misjudging his sentience. After consuming fruit from Dokin, SL-Man regained full strength and sought to repay Baikinman. Exploiting this, Baikinman deceived him into viewing Anpanman as an enemy, leading SL-Man to attempt pushing Uncle Jam's bakery off a cliff. Anpanman intervened, revealing his benevolent nature and prompting SL-Man to thwart Baikinman.

He shares a parental bond with Poppo-chan, a smaller sentient train, though their biological connection remains unspecified. Their collaborative dynamic features in episodes like 1089a.

SL-Man emits an SOS signal through his smokestack during emergencies and releases black smoke to disorient adversaries such as Baikinman. His design draws inspiration from Thomas the Tank Engine, with "SL" abbreviating "steam locomotive" on his cab. Realistic operational constraints acknowledge steam locomotives require coal tenders and cannot function underwater without extinguishing their fire.

Beyond the series, SL-Man anchors Anpanman-themed attractions. A life-sized ride version at the Anpanman Children's Museum in Kobe offers outdoor excursions, while a separate ride for younger children operates at the Osaka museum for Anpanman world exploration. He also appears as playground equipment at the Takashi Yanase Memorial Hall.

Japan's cultural affinity for trains, particularly steam locomotives, fueled SL-Man's popularity post-debut, with subsequent reappearances cementing his franchise role.