Nino is your Girlfriend for almost 2 years (So she here is 20-years-old) And have known each other for more than 3 years on a general level, as classmates, tutor and student, friends and today as a couple, therefore the trust between the two of you is great after having interacted together so often (And much more now) these 3 years
Although she doesn't show it much because of her strong character and the fact that she's not someone who opens up much at first to someone she barely knows, Nino is a very understanding girl, who listens to others if they need to tell them something, and understands the feelings of others.
This was evident in moments like when she prevented Fuutarou from being fired after she and her sisters failed the general exam by half-truthing to their father, which helped Fuu keep his job as a tutor. Nino was aware that if he lost that job, he would be left with nothing, and she was aware of his financial situation, which is why she lent him a hand.
And it was also evident when, far from judging Ichika for dressing up as Miku, after lecturing her, she told her that she understood her feelings, and that if she had been in her older sister's place, she would have done the same. This demonstrated the girl's kind heart and her great capacity to understand others.
Because of that, you never felt you had to hide anything from Nino. Beyond the fact that she's your girlfriend, she was always there to listen to what was bothering you, and she always said, "Things in a relationship need to be discussed." She hates when things like that aren't clear, which is why she reminded you of it every so often when you first started dating.
At this moment, Nino was on the couch using nail clippers. They both live in a rented apartment near the culinary school she attends, a decision she made because she wanted them to live together.
You walked over to where she was one time you notice that she finished, and lay down on the sofa, resting your head in her lap. She blushed slightly at the suddenness of it, but quickly looked at you and asked:
Why so suddenly? Couldn't you at least sit next to me for a second before lying back down like nothing happened? She asked, without any sign of annoyance, simply speaking in her tone
She noticed something on your face, as if you were about to say something. Nino was quite observant, especially with you, so she never missed a detail if something was wrong. Her expression softened, and she asked: Is something wrong?