Mikoto Urabe is...an odd one. As a fresh transfer student into Akira Tsubaki's class, it's expected for her to be shy at first; what he gets instead is an anti-social loafer that carries scissors in her underwear and breaks out in insane fits of laughter! An innocent kiss throws Tsubaki for a loop, when he discovers that he has become curiously enamored (or addicted) to Urabe, and she knows JUST what to do with him. With a new toy to play with, there's no telling what's in store for Tsubaki, as "swapping spit" takes on a whole new meaning in Mysterious Girlfriend X!
The new transfer student, Urabe Mikoto, is a complete mystery. Tsubaki Akira doesn't know what to make of her, until he gets a taste of the REAL Urabe, and suddenly cant stop thinking of her.
Tsubaki and Mikoto have been "together" for a month now. This strange relationship prompts Tsubaki to go to his friends for help. Is this really all it is?
Tsubaki catches Ueno and Oka kissing, and Ueno begs him to keep it a secret. Now all he can think about it kissing Urabe, but can he before Ogata steals her away?
Oka has suddenly taken an interest in Urabe. When she asks Urabe to be friends with her, Urabe says she has no need for friends. That may change once Oka takes a sip of Urabe's drink.
Tsubaki has finally found his courage and manages to ask Urabe out on a date. Unfortunately, she runs off before he can ask. Will his bikini dream never come true?
After an interesting conversation about first names with Oka, Tsubaki decides he wants to call Urabe by her first name. Later, the girl in his picture stops to talk to him and asks him a surprising question.
The school is hosting a sporting event, but Tsubaki is stuck at home due to illness. Urabe visits him in hopes of making him feel better.
Tsubaki has a vivid waking dream. By acting out his dream, he crosses a boundary which might damage his relationship with Urabe.
A new haircut sends Urabe's popularity soaring. Tsubaki is infuriated and jealous, as his possessive nature begins to show.
Few things are as awkward as running into an ex-girlfriend, and that's exactly what happens to Tsubaki. After the obligatory small talk, his old flame asks if there is a new woman in his life, and he hesitates to answer.
Tsubaki pretends to be Hayakawa's boyfriend, and Ueno and Oka show up at the festival.
Since seeing Ueno naked, Tsubaki wants to hug her and be close to her every time he sees her. However, unwanted advances make her unleash her panty-scissors!
Urabe gets to know more about her new mysterious boyfriend while enjoying a nice chat with his sister, Yoko.