Demon Lord Candidate

Demon Lord Candidate (魔王候補) is a title known to people who possess a Demon Lord Element, which can be in the possession of the person since birth or obtained through other means such as from the Sky Library. Throughout the series, only Arata Kasuga is known to be called that, despite many others being known to possess the Demon Lord Element later on in the series.

Demon Lord Element
An item which grants its user enough magic power to use extremely strong magical techniques that border the boundaries of Magic, such as binding an existence that does not belong to the world into physical form permanently. Known characters who possess/possessed a Demon Lord Element are:
 * Arata Kasuga
 * Lieselotte Sherlock
 * Lilith Asami
 * Abyss Trinity
 * All members of Malebranche
 * Deus Trinity

Hero Candidate
As always, when there is a source of malice, there would be someone who would stand up to them. Much details about them are not revealed yet, however, it is known that a Hero Candidate is an existence that opposes the Demon Lord. Known Hero Candidates include:
 * Mira Yamana

Later Mira ultimately becomes a True Hero, meaning she is no longer a Hero Candidate, and the source purpose of her power is to erase Demon Lords.