@gntz Girl thinks her life is perfect but one day they all wake up with numbers over their heads. Girl freaks out because hers is the lowest and she wants to be the best. Some delinquent says he knows someone who can help her but demands to get sucked off first. After she swallows his load her number rises, so she goes to find her boyfriend and fucks him thinking she can raise her number further, but nothing happens. That's the end of the chapter.
Yuina is a young teen who seems to have it all, she is an exemplary student with the best grades, role model behavior, good social skills and she has a boyfriend, Satoru. One day, after she has sex with her boyfriend something weird awakens in Yuina, she starts to see numbers above people’s heads.
This drives Yuina crazy as she soon starts to assume those numbers could be something along the lines of a ranking, and Yuina can’t stand her number being something so low as 248 which seems to be the bottom in the whole school as she looks around, she is obsessed with being the best at her social life, even at whatever this ranking seems to be, so she starts asking around the school if others can’t see what she sees, some people can see the numbers but no one seems to understand what said numbers might be, her friend tells Yuina she should calm down and just ignore whatever these numbers are, saying Yuina is already first at so many things so why bother with these silly numbers; but the resident Charao overhears Yuina.
Takahashi, numbered 48, approaches Yuina and says her has the answers to what she wants to know about but he will only tell her if she does him some “favors”, she resists his advances at first but Takahashi manipulates Yuina’s desire to always be the best and first in her school life, and so he leads her to the bathroom, while he said those things to her face in his private thoughts Takahashi can’t believe she is falling it so easily – he told Yuina that if they get “close and personal” she might rise in the rankings – and actually worked, she did him a “favor” alright; after finishing Takahashi sees Yuina fixated on the mirror, her number rose to 236, and his to 42, he tries to weasel more favors by saying their number might rise if they go any further, but Takashi is put off by Yuina looking at the mirror so he leaves.
Next we see Yuina and her boyfriend Satoru, number 126, and she is worried about Satoru saying anything about what she perceives as a low ranking hanging around her head, but Satoru comforts her saying whatever those numbers are, it doesn’t matter, he will love her no matter what; that gets Yuina emotional so she asks Satoru to have sex, they passionately do it, but after they get funky Yuina loses, she takes a look on the mirror and sees that her ranking did not change at all, unlike when she just sucked Takahashi off.
Sex with her boyfriend, number 126, doesn’t change her rank, but sucking a random numbered 42 did… anyone should know where this is going.
what can obviously be assumed is much like a few other stories with this base setup the number is not something good/strictly good and it isnt something that can be (easily) reasoned out from the limited perspective we have and MC has no interest in actually understanding the numbers even if it were possible for her to find out
my guess is the number IS some kind of social value but it doesnt track popularity. there is some negative quality that the other guy had that she started gaining through interaction with him. the reason her number was so high was because prior she had built herself to be the best and her boyfriend isnt as high a number because he's probably just a decent guy. if we saw more characters with distinct personalities we could get a better idea of what the numbers measure... though it isnt like the story is very interested in having us decipher the meaning as it's just an NTR vehicle
my favorite version was a comic where there were two numbers, one for how many people you slept with and another for the distance from the person you last slept with/the person you love or something
Assuming it leans more on the psychological and morally degrading side of the story then I'm in for the ride but if it's just going to be another mindless NTR... Well, not like we didn't see that coming.