The E-Bomb (髄爆, Zuibaku) is a magical bomb created using magical circuitry, magical rites, and materials mined from the world. It was an experimental explosive created by the Dwarves near the end of The Great War as an ultimate attack upon the other races.
Immense Power: It contained the power to kill an Old Deus. It is stated by Riku from the data he obtained from the Werebeast alliance, that the E-Bomb can destroy entire continents, completely destroy the surrounding Elementals, and even kill an Old Deus if unobstructed. While it overpowers the Aka Si Anse, it is only beaten in pure firepower by the Flügel's Heaven's Strike.
Ten Pledges: Due to the Ten Pledges decreeing that forbid war and violence, this applied to weapons as well. There are still E-Bombs in Harden Fell, however, they cannot be used as all mechanisms within it were rendered inactive.
Due to Riku's plan, the original plan to test the E-Bomb on the Lucia continent (with intent to completely destroy it) was changed to testing it upon Avant Heim and the Ariena continent, then going to destroy all other races. It was developed in facilities within Harden Fell as well as the Dwarf Development Facility.
At the beginning of the movie, when Riku was receiving data from the dwarfs, the E-Bomb was described as using fusion; if this was referencing nuclear fusion is not clear, but if it was then the E-Bomb could be considered a magically enhanced H-Bomb/Fusion Bomb. The ending suggests this is true due to the collision of the E-Bombs, Artosh's Heaven's Strike, and the Elvish Aka Si Anse resulted in apparently small star being formed.