SL-Man functions as a sentient steam locomotive for rail transportation, delivering goods and carrying children. His design draws from Thomas the Tank Engine, featuring "SL" on his cab to denote "steam locomotive." Initially discovered rusted and immobilized after a storm toppled a lightning-struck tree onto him, Baikinman later abducted him under the misconception he lacked sentience. Consuming fruit from Dokeen restored his strength, prompting a desire to repay the villains. Baikinman manipulated this gratitude by falsely labeling Anpanman an enemy, tricking SL-Man into attempting to shove the bakery off a cliff. Anpanman intervened, exposed the deceit, and proved his allyship, leading SL-Man to aid in foiling Baikinman’s scheme.

SL-Man is the parent of Poppo-chan, another sentient train; their familial bond was established after separate debuts within the narrative, making them the only two sentient trains. His capabilities include emitting an SOS signal through his smokestack during emergencies and generating black smoke to create diversions against foes like Baikinman. Reflecting Japan’s cultural fondness for trains—particularly steam locomotives—SL-Man achieved notable popularity post-debut, securing recurring roles. He stars in real-world attractions: life-sized ride installations at Anpanman Children’s Museums in Kobe and Osaka, where children ride alongside him, and as playground equipment at the Takashi Yanase Memorial Hall.

Unlike real steam locomotives, he operates without a coal tender and cannot travel underwater, as water would extinguish his fire.