origin={0,0,0};​​v1={.7,.4,.5};​​v2={0,0,1};​​VectorAngle[v1,v2]
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1.01568
In[]:=
basis=Orthogonalize[{v1,v2}];​​radius=0.2;(*adjustasdesired*)​​path[b_,theta_]:=Table[radius{Cos[t],Sin[t]}.basis,{t,Subdivide[0,theta,Ceiling[theta/0.01]]}];
Graphics3D[{Red,Arrow[{origin,v1}],​​Black,Arrow[{origin,v2}],​​Arrow[path[basis,VectorAngle[v1,v2]]],​​}​​,AxesTrue,BoxedTrue]
Out[]=