Just tossing more things to think about...
We know Yotsuba pretty much realized who Fuutaro was from Chapter 2 (Or we should see that in next chapter)
I'm guessing Itsuki realized that Fuu had met Yotsuba since Chapter 2 also when she found the pic of Fuu in his handbook when taking a drugged Fuu home?
Ichika realized Fuu was her first love Chapter 25, page 10 when she saw Fuu in wig at the test of courage.
I'm not sure about Nino... by the time she started calling him Fuu-kun she should have known eh?
But Miku... I thought she was the only one left out of the secret but now I'm wondering if she didnt already know before Ichika in Chapter 25??
So they all knew who Fuu was before the last arc in Kyoto happened?? And Fuu knew one (or two) of them was the girl in Kyoto.
We must be getting close to the end eh??
That question kind of hit me cause while this arc is having people probably look at older chapters to connect things with Yotsuba... it made me think that at end of arc when Ichika revealed she only realized Fuu was the boy in Kyoto only after seeing him in wig in test of courage, it made me look at chapters after that test of courage to see how Ichika react up until she told Fuu she was that girl. And some things made sense now like when they were both locked in the storage room in the next chapter and she cried for no reason and fighting her love alarm lol. She was already thinking of quitting school by that time and pursue her acting career... but later said she decided not to because she had a reason to stick around a little longer (and she outscored Miku in the exams

)
But what also made me think is Miku's reaction to Ichika seeing Fuutaro with the wig and her expression https://mangadex.org/chapter/85591/10
Before that scene she never really confronted Ichika about Fuu... but ever since that scene, she kept on questioning her feelings for Fuu... asking how she felt about him, asking her about if shouldn't it be her dancing with Fuu at the fire, and getting cut off when she asked if she loved him? Almost like... I see you realize that Fuu is the boy you spent time with in Kyoto 5 years ago... does Ichika still care for that boy? And then at times afterwards keep telling Ichika she's not gonna hold back... like trying to tell her if you don't pursue I am not gonna hold back... it's a fair fight now. And then at the last arc when Ichika goes a little crazy... it's Miku apologizing to Ichika that really confused me after her actions. And Miku also coming to some kind of understanding saying that if timing was a little different that it may have been her in that situation and gone crazy with her antics instead of Ichika. And also Yots saying she helped Miku being the most timid but if she really thought of the situation (remembering it was Ichika that spent time with Fuu in the past)... I mean it sounds like they all knew by then.
And at the end of Miku's arc they are all gathered around Ichika and she's the one getting consoled and concerned about her heart... What about Yotsuba??
Anyways, a lot of holes to fill still lol.