The royal family, followed by the royal knights, servants, and finally Aaron, were advancing towards the treasury. The treasury was located in the basement of the palace and could only be opened by the reigning 'king' or 'queen' of the time. This meant that only a person bearing the royal seal could unlock the treasury.
King Nerum possessed this seal, which had been passed down to him by his father, the previous king. His father, in turn, had received it from his mother.
If Aaron succeeded, he wanted to find some types of minerals that even interdimensional merchants couldn't obtain. Of course, this was possible, but he knew from his knowledge of interdimensional merchants that the likelihood of such minerals existing in Apollon's world was quite low.
If he couldn't find these minerals, he planned to obtain enchantment stones. If any of the enchantments he found were powerful, he intended to apply them to Night Will.