This particular secret realm was very important to him. It was a 'fantasy realm' associated with human consciousness, full of weird and extremely powerful phenomena that would be unthinkable and unimaginable in reality. Just like the cloud dogs that chased them just now, those really were clouds, just that weird and magical forces made them come alive. Aiolos and Mu Zi were afraid of them even if they joined forces; furthermore, these were the 'monsters' that were supposedly the easiest to beat.
What made Aiolos more anxious was that this fantasy realm was different from those that were recorded previously. This was a "fairy-tale world" based on human fairy tales!