Billy never tried to create a spell that could only counter another, but that was essentially what he wanted… So, he began to concentrate after enveloping his body in mana. Appraisal worked by relying on the eyes of the caster, so Billy thought of making his mana react when it felt being accessed by some outside source. After some attempts, Billy learned the final trick… He had to let his mana overflow outside his body to form the Aura that would be thin but powerful enough due to the amounts of mana to react to any unnatural use of mana on the surroundings.
Mental Armor: it grants you the power to counter the effects of identification spells. The cost will be the same as the level of the enemy identifying spell minus the level of your Mental Armor.
"What a redundant way to learn a spell… This was more mentally tiring than absorbing the armor," Billy thought.