User blog comment:B214/Question and Answers 2/@comment-24378967-20140122142943/@comment-1359322-20140122145106

We've seen that in Volume 9, it was pitiful.

Also like JJJ said, Ross is specialized in Norse Magic, so she could use that Magic Bombardment thing but it doesn't mean she is the only one who can do that. Any Valkyrie that is properly trained in Norse Magic might be able to do it too.