First Smile is the twenty-fourth episode of Engine Sentai Go-Onger.
At Hellgailles Palace, Yogostein mourns Hiramechimedes's death as the Vice Minster's ghost appears, frightening the Pollution Ministers. Meanwhile, the Go-ongers have emabrked on a camping trip, stopping at a Shinto shrine by a 1,000 year old cedar tree to wish for good luck. As Saki feels a sense of deja vu, the Ginjiro-go's engine breaks down, stranding the Go-ongers in the middle of the forest, where a spirit is believed to dwell. Saki suddenly sees a small boy hiding in the trees watching them, and follows him, thinking he may be lost. Suddenly, a monster attacks her and she transforms into Go-on Yellow. The monster is not a Savage Machine Beast, however, so Saki's counterattacks are ineffective and she is sent flying. She later finds herself tended to by the mysterious boy and promises to get him back home as the monster attacks them again. Meanwhile, the other Go-ongers are looking for Saki and run afoul of numerous youkai recruited by the ghost of Hiramechimedes, now calling himself Urameshimedes, as he is bent getting his revenge from beyond the grave. Scared out of their wits, Sōsuke, Renn, Hant, and Gunpei run into the Go-on Wings, and all six flee from the summoned onryō and run into Saki. Urameshimedes reveals himself, and admits to summoning the onryō and recruiting the monster Bakki from the Samurai World to battle the Go-ongers for him, with Earth's forest as payment. While the others fight the Ugatz, Saki learns that the boy is actually the very same forest spirit that she once met in her childhood. Bakki arrives as Saki transforms into Go-on Yellow. She defeats Bakki single-handedly with a forest spirit-powered Bullet Crash. As the boy returns to his tree, Urameshimedes possesses Bakki's body, enlarging it. Engine-Oh G9 is no match for the combo of Urameshimedes's mind and Bakki's power until Saki thinks to use a purified salt-infused G9 Grand Prix to both destroy Bakki and exorcise Urameshimedes. Yogostein resumes grieving, now that Urameshimedes is finally and utterly destroyed. Saki thanks the forest spirit once more for all it has done for her.