Reading the description, Danzel couldn´t help but have slightly suspicious that the skill [Soul of Death Essence] skill be involved in the appearance of the message.
As far as he remembered, the skill said that it made his soul more accustomed to dead mana itself. But it didn´t mention that the soul was fully accustomed to dead mana.
But now probably because of this skill, his soul should be fully accustomed to dead mana and soul affinity. Once the skill manifested, he felt more connected to himself, or rather his own mana.
Considering the sudden increase of the mastery of dead mana affinity and his soul affinity, such a change wasn´t surprising.
His own mana had always had a hint of soul affinity and dead mana in it.
Because of being undead, he could turn his mana more easily into dead mana than other types of mana. That also goes for what he calls "Soul Mana" which came from his soul affinity.
