Late in the series, we see that the war between Torumekia and the Dorok empire was fought over the technology kept in the crypt in the Dorok capital of Shuwa. Among other things, this technology includes cloning techniques, and the capability to extend human life far beyond its natural span. This was a very costly war to both sides. In particular Torumekia lost much of its army and was shown to be gravely impoverished.
When the Vai Emperor's troops fail to gain access to the crypt with artillery he forbids a proposed aerial bombardment, saying:
The contents of the crypt must not be harmed!
And when he learns that Ohma the God Warrior intends to seal the crypt forever, he stalls for time saying:
Wait! What do you ean, "seal the doors"?! We want to negotiate with them.
Once he gains access to the crypt, along with Nausicaa he meets the Master of the Crypt face to face. The Master informs them that the technology contained in the crypt needs to be preserved to rebuild civilization once the world has been purified, and asks for their help in this. Clearly part of the deal will include access to that technology. However Nausicaa flatly refuses, and the Vai Emperor is soon reduced to a bystander as they argue. Finally, Nausicaa
destroys the crypt, along with everything inside it.
Afterwards, the now-dying Vai Emperor expresses his admiration for Nausicaa and it is revealed that he sacrificed his own life protecting Nausicaa from the Master of the Crypt.
How to account for the Vai Emperor's abrupt change in perspective? Was it simply Nausicaa's charisma?