[Kirayuki]

Originally Posted by Reality Breaker

If Habaki and Zarasthustra both aim to kill Hajun, then why would the latter attack the former?

What has been said, the whole point is to prepare them for the fight against Hajun. And also

Spoiler for Throne:

Only one Hadou God can exist after taking the Throne. And Zarathustra know he is not the proper one for that.

Though I believe he would take the Throne himself if Habaki and the party didn't prove worthy enough.