User blog comment:Mich, Michele & Kuhla/Guide: UBB and the OD gauge/@comment-98.109.37.186-20150315145245

all 7 star units only need sbb 10 to unlock their ubb

There extra skill is the thing that requires speific things like the starters needing their GGC spheres to activate it or kikuri and sefia need there sphere's to activate their ability.