Eris' Evil Thoughts:
The Seal of the Saintess, protecting Solina's casket room, consists of 4 Guardians and 4 Powerful Devices. The Guardians, endowed with power from the Powerful Devices, can withstand attacks long as their Powerful Devices run. In order to defeat them, you have to weaken the power of the Guardians by destroying the four Powerful Devices. It sounds impossible, but there is no other way to meet Solina.
"Let me in."
"Tell me more about the Seal of the Saintess."
"Uh... Maybe I'm not quite ready yet."