Fake Itsuki, Miku, just wants to get Fuutarou to consider their relationship as something more than partners at this stage. But Fuutarou is dense ofc, so he took it the wrong way.
Funny how Yotsuba just blew her cover when he went to see them.
Then Miku as Itsuki tells Fuutarou that she wants him to be able to tell who she is, she proceeds to give Fuutarou hints, 2 of them, which are genuinely ways that Miku acts like, she wasn't bluffing or trying to mislead him. But ofc Fuutarou guessed anything else but Miku when he saw the hints, but it's NOT his fault. Nino has been acting very friendly and smiling alot, she even confessed, so it's no wonder he thought of her first, the second hint he guessed Ichika, which Ichika also loves him, so her interactions with him have also being quite indistinct from what Miku was showing. And then Miku gets angry and Fuutarou says she's acting like the real Itsuki.. i mean he's not wrong technically, if anything this shows Miku is kinda dense not noticing that her sisters have also taken some actions in the mean time. I mean she doesn't know about Nino, and so far Ichika has been interacting with her as if she's only a supporter, but really Miku, you had hints too. You've had 2 instances where you locked awkward glances with Nino, and Ichika giving advice like "first come, first serve" and then taking the top score in the exams. Miku you need to step up your awareness.
But yeah, Ichika has an ankle sprain, while Miku has the thigh injury, Ichika was the one trying to kiss him behind the car/van. So far it seems that Miku, Nino and now finally Ichika are all ready to push on their own individual love harder. Even Itsuki said she considers the relationship to had stepped up, in her case to friends... Wonder what Yotsuba is up to, she's still doesn't seem that involved.