WARNING: The following contains spoilers for Episode 2 of Girlfriend, Girlfriend, "How Nagisa Feels" now streaming on Crunchyroll.
The harem situation in Girlfriend, Girlfriend is gradually gaining speed in Episode 2, with the characters starting to become more fleshed-out and multidimensional -- especially Nagisa. Our first impression of her was that of an innocent, naive, kindly girl. But "How Nagisa Feels" starts to dig deeper into who she is and her personal motivations.
More than that, Episode 2 shows Nagisa's biggest weakness -- and it's actually Naoya. While Nagisa seems to have plenty of her own flaws, her devotion to Naoya is by far her most detrimental.
In Episode 1 of Girlfriend, Girlfriend, Nagisa told Naoya during her confession that she had spent three months working hard to improve herself so he would be more likely to accept her. This little detail flies under the radar until Episode 2 when Nagisa admits that during those three months, she had also missed school. This now leaves her friendless and quite behind in her studies. Naoya immediately offers to help her catch up and Saki joins in too.
But it becomes clear very quickly that Nagisa is very unprepared for school. When she couldn't figure out an answer to a math question, she holes herself up in the bathroom for more than three hours while she tries to figure it out in private. While she tries to play it off, she is really far behind compared to her classmates.
Saki thinks it would be a good idea for Nagisa to distance herself from Naoya and herself so that other students don't find out about their new relationship together. Nagisa has no problem with this set-up, despite the fact that she has literally no friends at school. The only people she knows are Saki and Naoya. But she doesn't mind being alone all the time if it means she can come home to Naoya.
All of this indicates that Naoya is Nagisa's biggest weakness. In order to win over his affections, she was willing to put aside her education and any other goals she may have had. Even now, as the new girlfriend of Naoya, she still puts his needs ahead of her own. She is willing to ostracize herself from the only two people she knows at school simply because it will make Naoya's life easier. She's also willing to jeopardize her future by slipping behind in her studies by three months all to make Naoya happy with her cooking and her body.
While Nagisa hasn't been fully fleshed out yet, she's starting to reveal more of her character, especially in the context of their three-way relationship situation. Ideally, she'll be more than just another anime girl who lives for her boyfriend, but so far, Naoya is the only thing on her mind, to the point that it's debilitating.