The Eternal sword has power over time and space. With it, Yggdrasill could change the very nature of the worlds. Perhaps he could even unmake them.

[Kratos shakes his head slowly.]

I don't know whether he can heal the rift between the worlds, with what's in his heart -- but I know he wouldn't. He would more likely take the Seed and leave, and let the worlds die, if he thought he had no other recourse. I cannot push him into a corner where he's likely to make that happen faster than he already is. And I cannot harm him myself. The seal prevents it.

And that's not accounting for the location. Yes, I will likely need continued access.

[Unless he can convince someone else to turn. Maybe -- no. Yuan has barely raised a hand against Mithos for centuries.]