>>713537670
Getting an UB rank is done depending of the stats + the amount of skills (that you buy with the skill points generated from the training, races and events)
Pic related has only three gold skills and four purple skills but 29 common skills (with two upgraded green-type ones)
I have a Christmas Mejiro Bright ranked at UB1 with 17 common skills, 8 gold skills and four purple skills as another example.