Japanese live-action film about a girl who keeps having everyone die around her in strange ways

Question

I remember I encountered this film while searching for something else on this site 2-3 years ago, and then proceeded to watch the first quarter or so of it on YouTube, but I don't remember the name of it.

At the beginning of the film, the protagonist, a high-school age Japanese girl, is on a bus with her classmates when there's a shot of something rushing toward the bus with the sound of wind. Suddenly, everyone on the bus except for the girl is killed rather gorily, seemingly by the wind slicing them in half. I think maybe the girl was saved by having gone down to the floor to grab a notebook? I remember her walking down the road in bloodstained white clothing, in shock, past dismembered bodies.

Then, she's at school and everyone seems fine (I don't remember how exactly the transition happened). She tries to explain what had just happened to her to her friends (three Japanese girls), but they assume it must have been a nightmare, right up until one of the teachers goes crazy and starts shooting the students, with the protagonist (and some of her friends?) escaping by running off campus. Either before or after the attack, the protagonist is terrified by the sound of the wind again.

Again, I don't remember what transition happened, but then she and her friends are in a set of woods by some water, and they're doing something with with a mattress (which they think might have been left by a homeless person?) and/or pillows, which I think has them either pillow-fighting, or tossing the bedding into the water. I don't remember exactly what happened there, but I remember they were talking about sex, with at least one of the girls proudly declaring all of the things she'd done (I think she was a stereotypical "rebel" girl, might have been taller than the others).

After that, I think I stopped watching it, but wound up looking up the film online, and learning that

The girl is actually a simulation on a computer in the far future, controlled by a sadistic middle-aged man, who might have been associated with her when they were in the same age, who gets his jollies from killing the simulated girls over and over, I think with the eventual goal of having sex with them. I don't remember what the page stated the resolution of the film to be, but I think she managed some degree of victory over her captor.

Answer 1

This is Tag (2015).

A girl's life cascades into chaos as everyone around her suffers a gruesome fate while she becomes less certain of who she is and her once-once normal.

The film begins with two buses full of Japanese school girls driving down a country road. Everyone on board seems happy and carefree and there's serene music playing, when all of a sudden, an invisible force accompanied by a gust of wind slices both buses in two along the horizontal axis, bisecting everyone on board, except for Mitsuko, a girl on the second bus who'd knelt down on the floor to pick up a pen she dropped.

She runs off in terror and eventually arrives at an all-girls school in a rural area, where some girls greet her as if they know her. One of them in particular, Aki, acts as if she and Mitsuko are best friends, and there's some talk about Mitsuko and Aki being virgins, while some of the other girls are apparently more sexually experienced. Mitsuko is still in a state of shock initially, but the other girls are all happy and carefree and manage to convince her that the incident on the bus must've been a nightmare.

Aki, Mitsuko and two other girls, Taeko and Sur (who's portrayed as being somewhat rebellious), decide to cut class and run off to a nearby forest, where they talk for a while and have a pillow fight with a pillow they find laying on a sheet on the ground. They return to the school in time for another class, when, out of the blue, the female teacher at the front of the class produces a minigun and unleashes a torrent of gunfire, killing every student in the room except for Mitsuko. Then Taeko and Sur run in, grab Mitsuko, and they make a run for it.

Following this, there's another incident with the wind, which Mitsuko is understandably terrified of.

Regarding the ending...

... it's revealed that Mitsuko is the main character in some type of video game being played by an old man sitting in front of a television with a joystick. I could say more, but I've matched more or less all the details mentioned in the question at this point, so I see no reason to spoil the plot any further. Also, the resolution of the film doesn't explain everything that clearly anyway; certain things are suggested, but you're left to draw your own conclusions to some extent.