@udomsa33 It's interesting but I don't think that's what happened.
Itsuki is Rena for sure when Nino should've remembered him and/or would'nt keep silence about it.
For the others, the charm Ichika mentionned seems a lie since fuutarou buyed five of them with Itsuki who then exchanged the one she had with the picture.
And since the picture was so important for Fuutarou, I don't think he could've lose something they shared like another charm we never heared about.
It let us with Miku and Yotsuba, the first don't seem the kind to drag someone she just met everywhere while the second could've just forgot she met him and stay silent if she remembered because it would harm the others.
My guess about Rena is that Fuutarou don't love her anymore but now have feelings for another of the quint, as the inn last chapter suggest. That's why he don't care about who Rena is anymore. He still got hints about it and now can exlude Nino, Yotsuba and Ichika
He may even already know about Itsuki and that's why he talked to her about Nino and Ichika loving him.
I'm just not sure if the author is a genius that give us that much hints because he knows where he is going or if he don't plan ahead and will screw the story.