Valentine's Day is approaching; Hosaka is still trying to express his love to Haruka by cooking, cross-dressing Mako-chan fears to be found out, Kana-"sensei" teaches the other girls how to "win" Valentine's Day, and Fujioka is desperately trying to receive Kana's chocolate.

The scene is Steam City, a London-ish city which represents an entire civilization run by coal and steam power. Because of steam, the city is sometimes covered in a mist. Villains take advantage of the steamy mist to hide and execute their evil plans. Only a few dare venture into what's beyond the steamy mist. They are known as the Steam Detectives: Narutaki (and his convertible all-purpose pistol), his nurse-assistant Lingling, and his Megamaton robot Gohliki. (Source: ANN)

The inhabitants of the village of Biaz, forced to labor in the serivce of the world-domination-happy Zein organization, hires Lina Inverse and Naga The Serpent to drive off the invaders. Lina and Naga agree, lured by stories of Elfin treasure sleeping below Biaz, only to get considerably more trouble -from the Zein and from the treasure - than they ever expected. 

(Source: ANN)