Vector3.Slerp normal

So I’ve started to mess around with slerping, and I understand how SLerp works where Vectors are treated as directions instead of as world positions. I have everything working the way I want it to, except I don’t know how to set the normal of the Slerp. Its best to show a pic:

There are only an infinite number of same-distance arcs when the two end points are on a line that passes through the origin. That is when they are 180 degrees apart when measured from the origin. If your start position is even a fraction of a degree along the arc, then you only have one shortest arc.