Got this idea from YoutubeJJunkie!
(Slightly changed it though)

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January 2, 2024

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I simply stare at the door. Is it really alright for me to go in? In the middle of the night? Putting my hand over my chest I take a deep breath and knock. It only takes a few seconds until the door is opened. But for me, it felt like years. Kirito looks at me shocked and confused. I glance at him. Then, I walk into his room wordless. Kirito looks like he wants to say something but decides not to. Once I am in his room he closes the door. Then he looks at me with a serious expression. "What happened?", he questions. I don't answer. I can't answer. Wordless, without changing my expression the slightest, I hug him. This startled him. Hesitantly, he puts his arms around me. "Do you want to talk about?", he asks me now. I shake my head.

"Was it a nightmare?", he asks. I slowly nod. I can feel my body trembling. How weak I am. I don't like it. "I know that you don't want to talk about it so I won't force you...but maybe someday?", he asks, patting my head which is resting against his chest. "Kirito?", I whisper, my voice cracking. This surprises Kirito. No wonder. I was quiet the whole time. "Y-Yes?", Kirito wonders. I grip his clothes tighter

"Am I a burden?"

"W-What? What ate you saying?! Of course no-!", Kirito tries to say. I look up, staring at him blankly.

"Am I better of dead?"

Kirito doesn't respond this times. He just stares at me with widen eyes. Then, suddenly he embraces me, pulling me to him. Holding me tightly. "You being alive...is the most important thing existing at this world", he mutters.

"Do you hate me?", I question, staring blankly at the ceiling.

"The one I hate is myself. Not you", he answers. I close me eyes and put my arms around his neck, holding him tightly. "Kirito?", I whisper, opening my eyes again. "Yes?", he responds.

"Don't leave me please."

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I hug Kirito. We are currently on his bed. I can't sleep. Slowly, I look at him. Kirito is already asleep, protecting me with his warmth. I look outside, not miving from Kirito's side. How familiar this scene is. But also oh so terrifying. I again, look at Kirito. But still. This time...I am atleast not alone. I glance at Kirito again. Then, with a determined look, I sit up. Moving to the side of the bed, I try to stand up. First, with one leg and then with the other. Once I am standing, my eyes widen. Immediately, I look at Kirito. Then I smile. Again, I go onto the bed. I stare at Kirito's sleeping figure. With my right hand, I take my hand in his. Then, I look at our hands, still smiling. Slowly, I close my eyes.
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"Thank you, Kirito."

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Yes, I know. Short chapter. The reason why I didn't really wanted to make a flashback of (u/n)' s past is because I want to give little hints and see how much you are able to combine them. In fact, I may actually really just give hints about her past. Though if, once the book is nearing it's end, you wish to get her full story, I can make a separate chapter were her story is told. I just think this is a more natural and better way to tell her story rather than the cliche, I have a breakdown and tell you everything, kind of thing. Especially since it doesn't match with the kind of personality I had in mind when creating (u/n)'s character.

Another thing. I am working on a game since my dream is it to be a game designer in the future. It is just some project and not a professional work but it means a lot to me. Since I am not only the game director of some sense, but also the only programmer and writer it takes much of my time to work on it, so I may not upload as often. I apologize. But I hope you can understand. Since the game is incredibly precious to me. I may only upload every two weeks from now on. Of course this can change sometimes.

Question:
I hinted something about (u/n)'s past. What do you think it is?

I can't wait to see some theories regarding this topic.^^