I like how Misaka is permanently bracketed at number 3 despite the huge power gains she's shown off at various times. She does manage to be reasonably circumspect.
As for how many Level 5s for how long, @REMasher, we know Mikoto reached Level 5 at age 12 and Misaki somewhen before her puberty and was one at 13 years old.
@REMasher actually i found there were 7 level 5s ever since the beginning of this series, i guess people who come from outside Academy City or came broken out of jail didn't know that
That card game scene(Page 6-9) is most probably foreshadowing.
I also love that Imagery in page 9
Touma= Joker, Accelerator = Ace,Kakine = #2, Mikoto = #3, and weakest card that can beat the Joker can also be Shiage
For this arc I guess Kimi will be the "Joker" since she has one the 8 Dragons inside Touma.
@InfiniteVerisimilitude First, a correction, general esper levels indeed have to do with power, going from able to bend a spoon all the way to be able to fight armies single handledly. What I meant is that Level 5 rankings are the ones that have nothing, or at least little, to do with how powerful you are.
To answer your question, Level 5 rankings are based on the importance of the Level 5 in question on the research of achieving SYSTEM/Level 6, that is reaching the level of a god while in a human body, the ultimate goal of Academy City. So even if Mikoto got "power gains" (which I really doubt she did in the first place), if it doesn't help further the plan, she stays as #3.