Devil Children Fire Book and Devil Children Ice Book are two versions of the same game within the Devil Children series. Released for the Game Boy Advance, each feature their own story line and cast albeit some overlap, most notably the main character of the opposing version (Jin for Fire Book and Akira for Ice Book, both of the aforementioned demon partners (Rand for Jin, Gale for Akira), Amy and Lena.
The game begins with towers leading to Makai and Tenkai appearing on earth, with demons and angels fighting each other to begin armageddon. Jin and Akira both try to find out what's up, with their demon partners returning to give them their aid. Amy appears and tells that Valhalla has been destroyed. She and Lena are then kidnapped, taken by Isaac and Mephistopheles to be taken to the angels Enoch and demon Zebul, and eventually their true masters. The two boys go on a journey through the demon and angel worlds to save them and stop the ones leading the forces of Fire/Light and Ice/Darkness.