Talk:Hero Crystal/@comment-99.162.150.197-20150416220106/@comment-24.113.206.59-20160208233128

It fills the red OVERDRIVE bar right above your items if you're using at least one unit that has UBB unlocked. It doesn't fill any of the units' guages, just lets you activate overdrive instantly. You would still have to activate Overdrive for a unit and use a fujin if you wanted to use a UBB that same turn.