This girl, shall we call her Ayase for now, has pink nails and longer bangs from chapter 23 onwards, until the accident. It's implied that chapter 23 is the earliest point in the story, somewhere around 2019 when she got the beret as a gift, which she would later rediscover on May 5th 2021, long after the accident, and use in chapter 1.
Chapter 34 implies that the accident caused episodic amnesia that got worse over time, until it became nearly permanent. All the things they do from chapter 1 to 22 seems to be the MC's attempts to get her to remember her past - buying her a copy or her own serialized manga, going to the same anime convention, the same cafe, the same arcade, letting her see her contact details on his phone, even wearing the kinky police outfit he bought her way back in chapter 23. She managed to remember it all on chapter 42, right before she opened the door. Just in time.
And then she says the line that turns this from an amnesia story into actual horror - "Then who is the woman at the door?"
Notice the graphical glitches at the top left of chapter 47. Near the front door of the apartment. Near the bubble speech where Ayase tells the MC that "his brain is scrambled" and that he can't tell what's real.
The MC might just be a brain in a jar living a simulation of some sort, and it glitched out at some point, creating at least two Ayases - the one from chapter 35, and the one from all the other chapters. They might have merged together when they met at the door.