Why do you think Vivenna is after Zahel and Nightblood?

[Adamkarma he/him]

Question above... I guess.

[+Invocation]

Because Nightblood is capable of drastically altering any planet he sets hilt on. That's not the kind of firepower you want out of capable hands, or at least out from beneath a very watchful eye. Vasher/Zahel just has a ton of knowledge that would be better to keep on Nalthis. I'm sure there are deeper reasons as well (Endowment may be using Nightblood as a cosmere-wide deterrent on invading Nalthis, for example), but even the shallow levels of reasoning are very solid footing.

[Returned he/him]

I've guessed that Nightblood was involved in something drastic on Nalthis, an atrocity or at least a massacre, at some point after Vivenna began carrying him. I doubt that Zahel or Vivenna was directly involved, but I can see Vivenna wanting to deal with that in some way (like trying to change Nightblood's nature somehow, or imprisoning him, or similar) while Zahel wants to remove Nightblood from the area to prevent further abuse or risk to Nightblood.

So he takes Nightblood and hops away from Nalthis, ending up on Roshar where he already has knowledge and connections. He hands Nightblood off to Cultivation, who can appreciate how dangerous he is, for safekeeping. He then disappears into the Alethi nation to frustrate Vivenna's search and draw her away from Cultivation, which works.

Something which I think has been underplayed in Oathbringer is that Vivenna has her own Awakened sword. That she has created one, especially without Nightblood's incredibly dangerous drawbacks, is a huge deal and we don't know much about what it portends. Vasher and Vivenna being in conflict, with that sword in the mix in the same place Nightblood is causing so much mayhem has to be significant.

Edited June 28, 2022 by Returned

[Stormtide_Leviathan]

This is probably a better fit for the cosmere thread channel than the warbreaker one, since it references events of stormlight archive