Board Thread:Manga/@comment-27321453-20200308161511/@comment-37493549-20200309182642

Neetaku wrote: So... Yelena's backstory is that she became disillusioned with Marley, and decided as a result to help Zeke euthanize Eldia? The point is without Eldians, Marley lose their titans. The only thing giving them the upper hand against the rest of the world. So she's both saving the world against any potential rumbling or return of the eldian empire, while also striking a huge blow to Marley's world dominance.

Like Pieck pointed out, she didn't really care about Zeke's motivations. She essentially only did it to become a celebrity.