Yiyen:
So impatient! Good manners never hurt anyone, you know... Oh, well, so you wish to know about the requirements for entry? Very well.
First of all, the magical characters above the entrance signify two people holding hands. I interpret this to mean that one person alone will not be granted entry. This glyph here...represents "mighty power." Perhaps the ones who enter must possess a certain level of strength.
Hmm...you can ignore the rest of these symbols; I'm sure they have no bearing on this subject.
...
To be perfectly honest with you, I can't actually read the rest yet -- but they don't seem very important based on their position.
(To enter, form a party of two characters who are over level 78.)
Enter the Dark Cloud Mansion.