Asa Akira always knew what she wanted to be when she grew up.

“I was obsessed with it,” Akira, now 28, recalls thinking when she was in middle school. “The girls were just really glamorous. They were having sex for money. I thought, ‘What’s better than that?’ ”

Akira has since appeared in more than 300 adult movies (the names of which are too filthy to reproduce here). She’s one of the richest porn stars in America, with a reported net worth of over $1.5 million. And in her new memoir, “Insatiable,” she’s unabashed about the love she has for the industry that has made her dreams a reality.

It has “shaped me into a woman I had always hoped I would be. I’ve become more confident, more empowered, more sure of myself than I’ve ever been,” she writes. “There’s nothing else I’d rather be doing.”

“I’m part of the new era of porn.”

Akira (a stage name) says her life story doesn’t fit most porn-star stereotypes. She had a “perfectly normal” childhood, with a doting stay-at-home mother and parents who have stayed together for 30 years. She was educated at the private United Nations International School in Manhattan.

“I’m part of the new era of porn,” she tells The Post. “We’re feminists, very sex-positive people. We’re not victims of rape, not drug addicts, we don’t have any daddy issues.”

About half the women in porn have similarly “normal” life experiences before entering the industry, especially now that porn is increasingly mainstream, she says.

Born in Manhattan, Akira lived with her mother and father, both Japanese immigrants, in Soho. Her mother stayed home to take care of Akira, an only child, and later returned to work in the nonprofit world.

Akira attended private preschool at Chelsea Day School. They spoke Japanese at home (Akira is fluent) and were health nuts. “I can count on one hand the times I was ‘treated’ to dinner at McDonald’s,” she writes.

Her family moved back to Tokyo when Akira was 9 because her father, a successful portrait photographer, was relocated there for work.

“Besides the moving around, I had a really normal, happy childhood,” she says. “Honestly, nothing happened to me that can explain all this.”

Still, Akira knew from an early age that she was more sexual than other girls.

“The first time I was called a slut was in fourth or fifth grade,” she says. “I didn’t know what it meant, so I looked it up in the dictionary and it said something like ‘unkempt woman.’ Unkempt? I didn’t understand.”

“I think, ‘What’s wrong with me? What made me gravitate to this?’ I know my parents must ask themselves that,” she says. “Once in a while I think I should go see a shrink to figure this out. But part of me just doesn’t want to know.”

She remembers taking a book out of the library about the reproductive system when she was in first grade and asking her dad, who was clearly uncomfortable with the request, to read it to her.

Judy Blume’s “Are You There God? It’s Me, Margaret” — a story of a girl’s sexual awakening, read by multitudes of young women with flashlights under their bed covers — left a “huge impression” on her.

She watched her first pornographic movie during a sleepover at her friend’s house in third grade. It was a soft-core movie based on a fairy tale. She wasn’t turned on, but she was intrigued.

Akira was 13 when her family moved back stateside to Downtown Brooklyn and later Clinton Hill.

Because her grandfather had spent 45 years as a Japanese diplomat, she secured a scholarship to attend the prestigious UN School.

“I was surrounded by the Manhattan elite. Spoiled trust-fund babies, and children of diplomats who arrived to school in black limousines with special license plates,” she writes. “And I was the scholarship kid.”

At night, she watched Howard Stern’s TV show on E! and became obsessed with the women he interviewed.

“Slutty girls were my heroes, somehow glorified in my mind,” she writes.

The UN School didn’t invite her back for her sophomore year because of bad grades, so she enrolled in the public Washington Irving School in Gramercy Park.

She worked as a cashier at the children’s bookstore Books of Wonder on West 18th Street, but secretly had other ambitions.

She scrolled through Craigslist ads, agreeing to a “sketchy” bikini modeling shoot when she was 14. She answered an ad for a “masseuse” but chickened out when the parlor’s owner asked her to “practice” on him.

Her eye was on one prize: Porn.

“But it was a far-away concept. I didn’t know anyone in porn. I wouldn’t even know the first steps to take. It’s like saying, ‘I want to be an astronaut.’ I wouldn’t know the first thing about being an astronaut,” she says, and pauses.

“I’m sure I’m going to offend a lot of astronauts with that statement.”

For her senior year, she transferred to the progressive public City as School, which requires its students to find internships to graduate. She first worked as a teacher’s assistant at a preschool, but quickly realized she “hated it, hated the responsibility of it.”

Then she landed an internship at the high-fashion magazine V. But that wasn’t for her, either.

“I’ve never been treated so badly,” says Akira, who has made films in which she has sex with seven men. “It was the most degrading thing I’ve ever done and I’ve done a lot.”

Working for high-fashion magazine V was “the most degrading thing I’ve ever done and I’ve done a lot.”

Thanks to one chance encounter after graduation, her life would change forever.

“Excuse me, miss?” a man asked her on the street. “Would you be interested in working in the adult entertainment industry?”

“It was like if you want to be an actress and [‘Kids’ director] Larry Clark approaches you,” she says. “I immediately said, ‘Yes.’ ”

That night, she worked a shift as a dominatrix at The Nutcracker Suite on 33rd Street.

Her first client, a pro basketball player, asked her to “role-play like we’re on a subway. I’ll like stare and stare at you, and you’re like totally creeped out by me.”

Other opportunities followed. A friend hooked her up with a gig at Larry Flynt’s Hustler Club, a gentlemen’s club off the West Side Highway.

The $600 (on a good night) she made at the dungeon no longer cut it. Now she could rake in up to $6,000 a night. She quit dominatrix work and took the stage name Akira, from an anime character.

Deep into a painkiller pill addiction, she began hooking, too, but quit after just two men because she got too close with one of her johns.

The stripper lifestyle began to sour on her, too.

“At first it was cool. I had never held so much money in my hand. But the novelty quickly wore off. I’m a bad salesperson — being like, ‘Hey, do you want some company?’ I hated that stuff,” she says.

She moved to Florida to work as a feature act on Bubba the Love Sponge’s radio show. There, she met porn star Gina Lynn, who offered her on-camera work.

“I knew that if I ever did one scene in a porno, it would change my life forever. So many jobs I can’t do now. I can’t do anything with children. I’m an only child, didn’t want to break my parents’ hearts,” she says.

Despite it all, she boarded a bus from Port Authority to Lynn’s house in Pennsylvania’s Amish country to shoot. Two days later, an agency flew her out to Los Angeles.

As one of the 5 percent of porn stars who are Asian (70 percent are white, according to The Internet Adult Film Database), Akira quickly discovered what typecasting means in porn.

“I can’t even tell you how many times I’ve covered my naked body in sushi, or played the role of a mail-order bride. ‘Masseuse’ is something I can practically list on my resume,” she writes.

There was an upside: “It pretty much guarantees me work until the day I quit, since there’s always a shortage of Asian girls in the business.”

She overcame her role as the “token Asian” by becoming a celebrated act in “Gonzo porn” — shot in close-up without much plot — for her extreme sex acts.

She decided to keep this new life from her parents, even though she found it highly unlikely that it would remain a secret. It didn’t.

Six months in, she got a phone call: “’We saw your video,’” they said. “I didn’t ask which one, so I just let it go. The conversation ended there,” she says. She never discusses it with them.

During her daily phone conversations with her mother, “I’ll be like, ‘Work is good,’ or ‘I’m going to work.’ But I’m not saying, ‘Hey Mom, I’m going to bang a bunch of guys tomorrow.’ ”

The money is good — the industry average is between $500 and $4,000 a shoot — but Akira claims it’s about more than that.

“Almost every time I shoot a sex scene, I fall a little bit in love,” she writes. “In love with being watched. In love with being on display. In love with being the center of attention.”

In many ways, hers are the travails of any actress or model. Weight issues are inevitable in a field where the average woman is 5 feet 5 and weighs 117 pounds. Instead of doing drugs and drinking, she consumes salads and smoothies, and practices yoga.

Sexually transmitted diseases are the biggest industry-specific hazard. She’s gotten chlamydia — a difficult thing to explain when you’re dating someone outside the industry, she explains. That’s one reason she’s now married to fellow porn actor Toni Ribas.

And then there’s the age issue. She’s 28 years old in an industry where the average is 22.

“I know the clock is ticking. I know soon I’ll be too old for this business and it will be my time to move on to something else,” she writes.

When she first moved to LA, she thought she’d spend two years in porn — most women only get three years in the business before they quit or are spit out — save up money, and then open a yoga studio.

Now she’s six years in and has signed a new contract with Wicked Pictures as a featured player (features have storylines and less close-ups on sex), a direction in which the porn industry in general is also heading. She’s also directing, another way to stay relevant and cash-rich in the new porn business.

Last year, she was invited to her 10-year high school reunion, but had to decline because she already scheduled her directorial debut — a group sex scene. “I told [my friend] to make sure to text me any good gossip — who’s gay, who’s rich, who’s broke, who’s fat, who’s on drugs, who’s dead,” she writes.

“Then I realized . . . Me. I’m probably the gossip. ‘Guess who’s in porn.’”