Itsuki:
"Fufufu... good try Nino, but I have the CHILDHOOD FRIEND card! Just wait to see how surprised he will be to see 'Rena' again!"
"Okay... that was a disappointing reaction... but once he finds out that 'Rena' is one of us, his mind will be blown."
"...uhm, at least I don't need to make him believe that I am one of the Quints. But look at how his gears will start turning when I challenge him!"
"... WHAT IS GOING ON?! THIS IS NOT AT ALL LIKE IN THE MANGA I READ! I AM THE FIRST GIRL! I AM HIS FIRST LOVE! WHY DOESN'T HE CARE ABOUT ME ANYMORE?!"
Funnily enough, this is a grave that Itsuki dug for herself. It was her own words that motivated him to let go of Rena and, true enough, he did not even think back on Rena since he decided to let go of her.
In any case, this chapter shows why Itsuki's victory is far from assured: Negi loves to subvert tropes. Not to mention that he actually has a reason not to let the First Girl win (First girl usually wins because for most, but not all, stories it is the most efficient trope, not because it is some mystical rule).