The original Leviathan died. However, in death, things are not necessarily over. The spirit of the original Leviathan finds its way to the body of Issei Hyoudou and from there, Issei Leviathan was born. Not content to wallow in old grudges, Issei Leviathan sets out to fulfil his original goal before his passing. To prove his dominance, as the one true serpent with no equal.