Catherine was hiding in a collapsed passage of a destroyed castle. It was one of the strongholds that got destroyed during the battle against DESTROYER. She came to this place after hearing a report about monster sightings in this area, but now she had to hide like a rat in order to save her life and dignity.
Catherine was a kind girl who was chosen to be one of the few World Oracles. Her status was very secret for the inhabitants of this world. The only reason she came to this place was because it was suspected that the monster living here might be related to the DESTROYER, so in that case that would need the ability of an Oracle to purify the corruption.
She herself did not have much of a combat prowess. So she had many guards with her to take care of that monster and also to protect her. And the mission went very well at the beginning.