There was a thread a week or two ago that pointed out that there is not much difference beyond fluff between a Warlock and a Magical Girl (such as the Sailor Senshi). They each have a powerful attack - and at higher levels can variate it a bit (different energies, shapes, etc) as well as gain some other useful abilities. They can take a lot of damage (DR, energy resistance), heal surprisingly fast at times (brief Fast Healing), etc.
The thread tapered off, but it eventually basically stated that a female Warlock - if the fluff was altered and if they took the Summon Familiar feat (or, if in a group, at least one had the feat) would basically be a Magical Girl. Oh, and if the AL was altered to suit the new fluff, of course.
Perhaps at first level the damage type of the Eldritch Blast is altered to fit each magical girl. Mars gets Fire, Moon gets the basic blast (thus not needing to worry about energy resistances), Mercury gains either Cold, Jupiter gains Electric, and Venus gains Piercing (as she tends, from what I recall, to be more of a Soulknife variant anyway). So Venus' is weak against normal DR/- and DR/piercing, but can ignore energy resistances like typical weapons. Moon's is weak against nothing really, while each of the others is strong against one element but weak against another (Mars vs fire type creature or vs a cold type creature, for instance).
It would need more tweaking, but it is nicely setup, I think. Their continual adventures build up their levels, and they moonlight (if you'll forgive the pun) as 'normal' kids most of the time.
If you want to make it odder yet, use Binders, with the benefits coming from the planets to which they are bound acting as vestiges. Perhaps there are several variant vestiges of each planet to define the various power levels. Or perhaps when they call out 'Crystal Makeup' or whatever they are binding to multiple vestigest of a single style / planet - thus explaining the increase(s) in power. As with Warlocks they increase in levels over time, gaining the ability eventually to be more powerful from binding more potent and simply more variants of the vestiges of their planets. You will have to create all new vestiges, however, and multiple ones for each planet besides. It would be easier, I think to simply use the Warlock idea.
You could also use a template, I guess, but considering the various differences between the magical girls you would need a different one for just about each one. Warlocks, if altered a bit, can suffice without that - just have each one choose a different style of eldritch blast at first level to suit their nature and at later levels limit their choices (or create new choices) to better suit their growing nature.