The seal was already broken? Oh my...

We must defeat Crocell before he causes further harm to others.

In order to do so, you must go to the location where Crocell is. Oh, before that, did you say you had the Old Key you received when you acquired the treasures?

There is a Treasure Chest in the Basement, but I can't find the key to open it.
This is just a humble opinion of a Pirate, but I think the key you have may be the key to that Treasure Chest. I think the demon is taunting us.

Could you go check and bring me some clues?

You don't have much time.

So, indeed, it was the chest that Crocell left.
Show me the treasure that was inside the chest.

Let's see...
I'm certain that this is the emblem of Crocell.

Oh, and when you were trying to get the box opened, I found Crocell's hiding place.
But I couldn't go inside because of a powerful magic force. The emblem you discovered may be the key to the Demon's Doorway. Crocell is taking us for fools. She's challenging us to find her if we want...

Open the box in the Basement.