@Big_Boss
As Itsuki said in this chapter, This is not the end of the manga, hell it might not even be Yotsuba, But in terms of developement, she is literally the first one to warm up to him, which means first to develop, Her story is just more complicated than the others and require more development.
First girl is a bit ambigous in this manga, First to meet, Itsuki, First timeline wise Yotsuba, First to fell in love storyline wise, Miku
@pippo311lp
This is part one of Fuutarou story, so probably next part. Also Fuutarou is not as dense as we thougt to be, remember, he know Miku likes him for quite earlier than expected. He hesitate about something when describing Yotsuba to Rena in the boat? meeting. So I expect some I know you have been the one all along or some stuff.