Unlike Jack, Jun does not have a calm reaction to the situation. Not calm at all. When Yuui entered the room she was startled, and upon not recognizing him she freaked. (Honestly, she shouldn't have been skipping classes since her arrival at the school). But now she is on fire, things are on fire, and Jack's bed is on fire. It's probably a miracle that Jack isn't on fire. If either of them tries to go near her the fire will get much more intense and start to spread. Thankfully she isn't burned by it all, but that doesn't mean Jack or Yuui won't get hurt.