How does Zacian's ultimate ability work?

On mobile at least, it seems like the auto-aim is off. For example, all of the enemies are on one side and the ultimate would aim the opposite side. I thought maybe the ability automatically aims the direction zacian is facing but I've seen cases where it would aim backwards from when I cast the ability. It doesn't seem like you are able to aim the ability once the ability activates due to the charge feature. Is this a bug?