She is irreleavant. Sur she gave him his complex about like Hina dolls, but we're past that now. She could have never been introduced and the story wouldn't have been worse. This is another stupid additional character that we have to pretend is a potential romantic rival until she disappears like all the rest.
I really don't think she is irrelevant to the story, though. She is the reason he had a complex about people in the first place...because he didn't want anyone to know about his like of Hina Dolls. He then met Marin who was so enamored with the fact he was doing what he liked that she saw nothing wrong with it, thus leading him to accepting himself more (but still harboring some trauma). He can't be his best self while holding on to the trauma, and throughout the series we have been reminded that it still exists. Hell, it was seen recently with Comiket...he thinks that the shining star is Marin here and his creation is second when the reality is that it is both things coming together to make it the shining thing.
I think seeing things from Non-chan's perspective puts everything into place. They were children, they don't really know how to express their feelings properly OR talk things out like adults would so I am not surprised that things turned out this way. I actually shed a bit of a tear for Non-chan because she just wanted to be of help to him and felt that because he was looking at Hina Dolls she did nothing for him, when I bet ANYTHING that he only came out of the room because she would go there every day and read/talk to him without any expectations that he would respond. He just had been unable to say it then because of being blindsided by her telling him she hated him.
As for Marin, well, she has always been like this. Feeling like she is a burden on him because of how devoted he gets to the craft. I really do hope they talk it out instead of her going off on her own. These two are so close yet so far sometimes...and the recent chapters where she talked to his grandfather, Gojo just needs to see what everyone else around him sees instead of being wrapped up in his inferiority complex....
Which leads me to this: I hope the point of this arc is that him and Non-chan make up and she apologizes for what she had said and tells him why she said it as well as being the catalyst for him to see the things he needs to see and makes up with Marin and instead of pursuing being a Kashirashi he devotes himself to more cosplay for Marin. I really do think that his grandfather is absolutely proud of the cosplay he has made and sees that Gojo is a fine craftsman who probably outshines grandpa, but Gojo is tunnel visioned into the Kashirashi thing that he can't see beyond that to realize he is amazing in his own right.
