The group of demons seems very powerful which makes the two hesitate a little due to their limited knowledge about them as they knew nothing about what type of demon they may encounter.
They both knew how powerful demons were and even if Aron did say that he had seen a lot of demons before they came to this world, he knew that only by experience could he tell what kinds of demons he'd see here.
Riku looks over at Aron as they stand side by side before taking a deep breath, telling herself that she must calm herself and not let any demons get the best of her.
Aron on the other hand takes a deep breath to remind himself to breathe, not because he was trying to be cool, but rather because he was nervous and it's making him anxious as fuck.
Creation is hard, cheer me up!