>Miku put a stop to her bullshit.
Thats a funny way to type Itsuki who did it because she cannot stand hard work going to waste (as she recognized that he did worked hard and did not deserved that) and Miku was the one that cornered Nino to begin, in fact even before Itsuki told us directly that Miku and Nino tend to butt heads and we saw that before.
Also for the ones complaining about Nino, right from the start she was against Fuutarou being their tutor and I guess anyone else being their tutor, she been very defensive of her family from the start, Nino behavior been mostly a reaction to Miku taking Fuutarou over her and the fact is, Nino is family ... Fuutarou is not, having her sister taking a stranger side over her is going to hurt her and in case anyone forgot, they are 15, you should not expect maturity, they are all brats.