The secret words in the cypher... Its almost like the ancient people knew that English-speaking peoples would find it one day. But why include those specific words? And they must've also known that the computers they had would not have been able to decipher the messages completely.
Nice, but a typical RPG Maker MV game. I'd recommend trying to make your own GUIs or tilesets. Though you used Yanfly's text plugin well, I'd recommend trying to make your own resources. Sorry if this offends you in any way, I'm just giving you a suggestion. If needed, I'd be more than happy to help.