Forbidden Magic 「禁術魔法 Kinjutsu Mahō」 is a classification for spells that draw power from the underworld.
Forbidden Magic spells make use of negative mana 「負の
Forbidden Magic can also permanently alter the souls and magic of users and victims. Licht's demonic transformation, the highest level of Forbidden Magic, destabilizes his soul so he is not fully awakened by the Reincarnation Magic. It also tainted his magic, as well as the magic of Lemiel who absorbed some of Licht's monstrous magic. Elves who succumb to despair and are influenced by Forbidden Magic become dark elves. Even if they recover mentally, their soul and magic remain altered. Humans who overuse Forbidden Magic risk developing Weg—a pair of black horns—and losing their humanity.