That was the Essence of Flame gifted to him by Baro's master, Kaldu; most of it had been refined on the spot, leaving only a small part of the essence within the essence untouched. This essence had emerged during his Foundation Establishment, attempting to transform Lancelot's body, but many of the Spirit Stones he used for his Foundation Establishment were provided by the Succubus's Angel lover, which contained the Spiritual Energy of the Heavens that neutralized the influence of the Demons' gift.
At the time, Lancelot thought the hidden dangers of the Demons' gift had been resolved. It seemed that was not the case.
More shadows rushed towards him, and the anger in Lancelot's heart grew even more intense. Since this was his own rage and not the effect of an external magic, the defense prohibitions in the bamboo slip were not activated.