So right now it's between Yotsuba and who ever was with Fuutaro when Yotsuba and Nino saw them in the hallway everyone else is out of the picture for now since he basically cares about the girl that was in the photo the most which is between 2 people Yotsuba who shared the memory of making the promise and the other one who shared the memory of playing with him till someone came and picked him up stil who is the 2nd one :/
Ch 83 page 5 - Ichika confession she was the girl from 5 years ago.
https://mangadex.org/chapter/595924/5
Ch 85 page 14 - ichika's memories of that evening 5 years ago along with her memory of the day she realized Fuu was that boy in Kyoto during the test of courage.
https://mangadex.org/chapter/614118/14
Ch 86 page 10 - Flashbacks of all the special moments she shared with Fuu including the time she met Fuu in Kyoto in the top right diamond panels.
https://mangadex.org/chapter/619757/10
God even in this chapter we saw how they had developed her story and why it was all so interconnected.
Jeeze in retrospect this was genius and the Yotsubro conspiracy theorists were right all along.