Disabled during a storm when a lightning-struck tree falls on him, SL-Man is discovered unconscious. Baikinman mistakes him for a non-sentient object and transports him to Baikin Castle. SL-Man regains consciousness and strength after consuming fruit provided by Dokeen, leading him to feel indebted to Baikinman. Exploiting this gratitude, Baikinman manipulates SL-Man into believing Anpanman is an enemy. Under false pretenses, SL-Man attempts to push Uncle Jam's bakery off a cliff. Anpanman intervenes, reveals Baikinman's deception, and convinces SL-Man of his true heroic nature. Following this, SL-Man aligns with Anpanman and dedicates himself to transportation services.

His primary functions involve delivering goods and transporting children across various locations. He operates effectively on both railway tracks and standard terrain, utilizing articulated arms for mobility. Specific abilities include emitting an SOS signal through his smokestack during emergencies and generating thick black smoke to disorient adversaries like Baikinman. His design draws inspiration from steam locomotives, notably Thomas the Tank Engine, with the "SL" on his cab signifying "steam locomotive." A limitation within the series' logic prevents him from operating underwater, as it would extinguish his firebox.

SL-Man considers Poppo-chan his child, a bond highlighted in later episodes like 1089a. He features in multiple Anpanman films, including a 1995 ghost ship storyline where he counters Baikinman's aquatic threats. His prominence extends to real-world attractions: life-sized rideable replicas exist at the Anpanman Children's Museum in Kobe and Osaka, with the Osaka version catering to younger children for tours. He also appears as playground equipment at the Takashi Yanase Memorial Hall. Merchandise includes push-along toy cars modeled after him.