Quite an interesting story which could be explained with many narratives. The numbers can be explained with at least 2 ideas, that is: they're lies and they tell how much is our charm.
1) They're lies: You can expect the 3 characters that were brought in for example (the ruthless boy, the jocks and the nerd). It makes sense somewhat for their personality to have that number above their heads. It also makes Aikawa a much more intriguing and nuanced person since she tells so many lies a day in comparison to other characters. You can also notice when she lies by the number above their heads.
2) They're charm: Again, obviously makes sense for all the characters to have their numbers. But if Aikawa's statement of "love can make one more charming true" then perhaps the reason why our MC's numbers increase is because of his crush on Aikawa.
Anyways, just my 2 cents. ¯\_(ツ)_/¯