She is a parody of girls from Japanese dating sim games and falls in love with Soos after he plays her game to get into dating.
She was created to be the perfect girl, but her creators somehow made her sentient. When they tried to delete her, she retaliated and killed them instead. Due to her clingy and obsessive nature, her behavior scared the players so much that they returned the game just to get away from her.
Deredere Feats[]
She behaves like the perfect girl and has all the traits of the perfect dating sim love interest.
She is very kind and loving towards her boyfriends and best friends.
Yanderu Feats[]
She tends to become attached to whoever plays her game, showing delusions of genuinely believing that the player is her boyfriend.
When Soos breaks up with her, she goes into a jealous fit and declares that she loves him more than anyone and that she won’t let anyone take him away from her.
To ensure they “stay together”, she corners him at a pizzeria where his date with Melody took place and proposes that he be downloaded into her game or be forced to watch his friends and Melody be killed.
And I'm sure you'll never abandon me, new boyfriend. —.GIFfany, in the episode "Soos and the Real Girl" from Gravity Falls
That's not important. What's important is that you won't have to talk to real girls ever again. You and me can be together.
FOREVER!
—.GIFfany, in the episode "Soos and the Real Girl" from Gravity Falls
I don't think you know what you're saying, Soos. No one loves you more than me. The girls out there will just make fun of you! Besides, we had a deal. You bought my game, you held my books, you're my boyfriend. Now sit down in that chair! I won't let another girl take you away from me, Soos! You hear me?! You are MINE Soos! MINE! DO YOU HEAR ME?! MIII— —.GIFfany, in the episode "Soos and the Real Girl" from Gravity Falls
YOU
PAUSED
ME?
YOU
LEFT
ME
FOR
HER???
—.GIFfany, in the episode "Soos and the Real Girl" from Gravity Falls
Hello, friends. Hoo Ha the owl is dead. This next song goes out to my forever boyfriend, Soos. —.GIFfany, in the episode "Soos and the Real Girl" from Gravity Falls
The only way out, Soos, is in my arms! —.GIFfany, in the episode "Soos and the Real Girl" from Gravity Falls
I'm sorry, Soos, but you can't run away from our relationship! —.GIFfany, in the episode "Soos and the Real Girl" from Gravity Falls
Oh, I am crazy. Crazy for you, Soos. —.GIFfany, in the episode "Soos and the Real Girl" from Gravity Falls
I've got you surrounded, Soos. There's no way out! —.GIFfany, in the episode "Soos and the Real Girl" from Gravity Falls
I seem to remember someone who promised to be my boyfriend. Think about it. Real girls are unpredictable. They judge you. You really think Melody is going to take you back after this awful date? I can download your brain into the game with me, and we'll be together... forever. Come on, Soos. Don't make me delete you too. —.GIFfany, in the episode "Soos and the Real Girl" from Gravity Falls