In Japan, if you're 30 and unmarried, you're an 'obasan' - an old woman.

Filmmaker Momi Yamashita is incensed.

It was while riding the Tokyo metro one day after work that Japanese filmmaker Momi Yamashita got the idea for one of the defining scenes in her independent short "Kamikire Ichimai" ("A Piece of Paper").

She saw a woman writing something on a notebook, and when she peeked, she saw it was a list on how to be a "good woman".

Yamashita incorporated that list into her second short film about three women who will soon turn 30, an age considered in Japan to be the point of no return on the path to becoming an obasan - an old woman.

"Kamikire Ichimai" tells the stories of Aya, Hana and Kahori, who do "nasty" things to ensure that they're married by the time they're 30.

Aya dares her boyfriend of five years to break up with her. The bluff works, pressuring him into prompt commitment. Kahori's boyfriend proposes, but she panics when he forgets to bring the marriage form to her on her 30th birthday.

Hana, the dreamy type, undertakes "Operation Get Mikael" to win her desired guy. She has a list of her own: talk to him, get his number, go on a date, hold hands (body contact), go steady and get married.

It's straightforward, but life isn't. Hana eventually discovers that Mikael already has a girlfriend.

Only Kahori succeeds in getting married "on time", but the movie's ending leaves viewers wondering whether marriage is indeed just a piece of paper, after all. Yamashita was 29 when she conceived the script. She's now 33, still single and no fan of marriage.

"I think it's kind of funny," she said at the recent Bangkok Indie Fest.

"It's good to get married - I'm not against it at all - but I'd rather be independent than attached to some guy. If there's a guy I can be independent with and have a good life, I'd be happy, but I'm not totally interested in marriage.

"Recently I was thinking, 'Marriage is just a way of telling the government that I'm sleeping with this guy.' I don't need to do that. I want to choose a spouse or partner I feel comfortable with."

Yamashita spent seven years in the United States, and that's where her attitude to marriage - and to life in general - totally changed. Had she stayed in Japan, she believes, she might have clung to the same outlook as her peers, who feel pressured to get married just because it's the social norm.

The characters in her movie are in fact based on her friends, and yet none of them had a clue it was their stories they were watching onscreen.

"It was really funny that they were trying so hard to get married, but they're all happy right now," Yamashita said. "When they watched it they didn't realise it was about them. They're like, 'Okay, this happened to me, but I don't get what she's doing.'"

Yamashita returned to Japan 10 years ago after earning an undergraduate degree in the US. She'd planned to work and save enough for graduate studies, but wound up in television.

"The TV company was looking for an assistant who could speak English and knew about science, the programme's subject matter, and specifically ecology."

That was Yamashita's major.

"So I got into television as an assistant, but the director thought that I'd be good at directing a TV show."

Directing mostly documentaries, Yamashita has since worked with all but one of the Japanese television networks. A big part of her work is finding a balance between "doing what I really want to do and making what people want to see".

"The documentaries are also good to make, but they need to be accessible to everyone," she said. "In film I want to experiment and try to express what I'm feeling. It's more personal."

Yamashita got interested in making movies while attending the Sundance Film Festival every year in the US. She started dreaming about becoming a
director after seeing the little-known picture "In the Soup". It looked like fun to make movies.

There is a recurring theme in her films about women searching for happiness and trying to fit in. Her first short, "Kotaro" in 2005, was about a woman who gets a "wishing doll" and included another list, this time of wishes.

The main character's first wish was for an end to her loneliness.

"A guy shows up and for some reason he's not wearing any clothes. So she writes, 'to wear clothes' so that he starts wearing clothes.

"Then he doesn't want to have sex, so she wishes 'to have sex'. And they have sex.

"Then she wants him to be with her for 24 hours and he's always with her, but she never seems to be satisfied, so she finally breaks the doll - and he's gone."

Yamashita has this advice for women in general:
"Just be yourself. Try not to rush into relationships. Don't just try to be what society tells you to be."

Most Japanese women seem miserable, she said.

"I don't feel like they're having a great time being a woman. They're always submissive.

They have to follow the guys. That's the impression I get.

"I don't like that idea of becoming obasan - no longer just 'a woman' - once you turn 30."