Yes, I know Plants Vs. Zombies came out in 2009 and this fic would be set in either 2001 or 2002. A theme park guide in the manga during Chapter 16 says the year is 2000. And that's during the second year. This fic, though, is set in the third year.
I've decided to make this fic listed under "Plants Vs. Zombies" as a fandom even though in the world of this fic, it's an in-universe video game.
In the senior year of Sakaki, Chiyo Mihama, and their friend group's time in high school, a new video game for computers had released where zombies were attacking your house and you planted plants to fight back. What was it called? Plants Vs. Zombies.
What made the friend group that didn't have a name (the other members besides Chiyo and Sakaki were Kagura, Koyomi "Yomi" Mizuhara, Tomo Takino, Ayumu "Osaka" Kasuga, and maybe also Kaori "Kaorin") get interested in this video game was a particular mod for it that replaced the zombies' heads with that of a gray stray cat that kept biting Sakaki's hand when she tried to pet him. In her head, she gave him the name "Kamineko", but it was a descriptor that she meant to mean "biting cat" (though it could also mean "god cat") and it was possible he lacked a real name given that he was a stray.
The download page for the mod claimed that, in the context of the mod, Kamineko somehow found a cloning machine and made several clones of himself that had humanoid bodies. It also had a disclaimer saying that all likenesses used in the mod were used in a fictitious way.
When Sakaki played it, she found it creepy that whoever made the mod knew a lot of details even with the disclaimer. They also replaced a character that served as a shopkeeper and part of the tutorial with Chiyo, using a feminine voice speaking English to replace the gibberish the original character used. All of his (the original character was male) dialogue was changed as well.
The real Chiyo walked up, saw her likeness in the game, and asked, "Miss Sakaki, why am I in that game?"
"I don't know. I think someone altered the game. Besides putting you over one of the characters, whoever made this also replaced the enemies' heads with that of Kamineko,"
"What do you mean replaced?"
"This isn't the original game. This is an altered version of it-" but Sakaki heard a scary jingle to signal that she had lost and a Kamineko headed zombie got into her character's house. More of the same biting sounds played as they did when the Kamineko clones took bites out of the plants and green text appeared that said, "Kamineko Went For Your Jugular!"
As that text appeared, audio played of Sakaki screaming like she did when she saw a cockroach loose in class during her first year of high school. Seconds later, it said, "Game Over" with a button underneath that said "Try Again". In the top right corner, there was another button that said, "Main Menu".
Sakaki said, "Okay, I think that's enough,"
She disliked how it used her likeness and that of her friend without their consent, but since she was quite timid (many mistook her shyness for being aloof), she had no plans to get the mod taken down.