Board Thread:General Discussion/@comment-24815992-20140415163141/@comment-5398287-20140415165134

Well, that's kind of one of the requirements, in a sense. You know how the seats in a division are organized by power (with exceptions like Yumichika and little Gi), right? Well, the captain is the most powerful out of all of them, and they each have a spiritual power that easily surpasses their lieutenant. The methods for becoming a captain tie into this: having a Bankai (simply achieving Bankai increases your spiritual power drastically), being recommended by 6 other captains (they wouldn't recommend you if you didn't have enough power to be a captain, in addition to other things), and defeating the current captain in single combat (you wouldn't be able to beat them if you weren't roughly at or above their level of spiritual power), hence the baseline power level for the captains on the wiki. Hope that helps.