User blog comment:B214/Volume 17 spoilers./@comment-117.217.186.212-20140224111716/@comment-24468758-20140225221830

Do you really think someone who learned enough of norse magic in one day to oppose a norse god lacks enough intelligence to do that on his own? Vali is very intelligent he just likes to hide it because of his behaviour as a battle maniac, which is quite the opposite of Issei who could make good use of such an ability as he won't seem intelligent whatever he tries.