“Madoka! Madoka!” a man shouted, and the 16-year-old dressed as a 14-year-old Japanese cartoon schoolgirl stopped in the middle of the Baltimore Convention Center. “Can I take a picture?”

She nodded, then struck a pose as Madoka Kaname, the “magical girl” character she was dressed as last weekend at Otakon, the annual festival of Japanese cartoons that once again turned the Inner Harbor into the epicenter of all things anime.

Her costume included a Day-Glo pink wig with pigtails, white knee-high stockings, a red choker and a short pink-and-white dress that Little Bo Peep might have worn on a day she wanted to alarm her parents.

The man, who appeared to be in his mid-30s, pointed his digital camera at the make-believe Madoka, snapped a photo . . . and then stared.

And stared.

“It can sometimes be very weird,” the teenager said of her convention encounters with overly interested older men. “But they really don’t mean any harm.”

This is a delicate time on the anime convention circuit, where a demographic shift has created an occasionally unseemly and sometimes dangerous dynamic.

The first Otakon, held in 1994 at a cozy Days Inn in State College, Pa., back before the Pokemon movies and “Spirited Away” and the Cartoon Network’s anime programming, drew just 350 people. Otakon is now the largest anime confab on the East Coast; this year, a record 31,348 turned out for the annual Japan-centric nerd-out at the 1.2 million-square-foot Convention Center.

Men have long been the foundation of the genre’s fan base, but they’ve been joined in increasing numbers by teen girls, whose embrace of the medium’s more fantastical side has helped launch anime to new levels of stateside popularity. Conventions that were once cult gatherings attended almost exclusively by VHS-trading college-age (and older) males are now overflowing with young females, many of them sporting various iterations of anime’s popular doe-eyed, scantily clad look.

The dark side of the new demographics has not gone unnoticed.

“The Con perverts,” read the title of a Web forum thread that catalogued alleged stalking of minors at anime conventions. “Ever happen to you?”

* * *

Last month, a 34-year-old Silver Spring man admitted in federal court that he had sex with a 13-year-old girl he met in February 2010 at Katsucon, an anime convention at the Gaylord Hotel at National Harbor in Prince George’s County. Michael A. Alper, who had previously been convicted of raping a 13-year-old in Virginia, pleaded guilty in U.S. District Court in Greenbelt to coercing and enticing a minor to engage in criminal sexual activity.

The news spurred Katsucon organizers to announce that they might begin checking their convention pre-registration list against sex-offender registries before their next event. Under the proposed policy, anybody listed on a published sex-offender registry would be denied entrance to Katsucon, which returns to National Harbor in February.

“We want to make sure we stay within the ethical and legal guidelines afforded to us in Maryland, but at the same time do everything in our power to protect our most vulnerable attendees,” Katsucon spokesman Chad Diederichs said.

Jennifer Piro, a member of the board of directors for Otakorp, the nonprofit group that produces Otakon, said that “no decision has been made” to introduce a similar policy at their convention.

Otakon, she said, has taken precautions to protect minors. All attendees younger than 12, for instance, must be accompanied by a parent or guardian at all times, and adult-themed programming is presented late at night, for those with 18-and-over wristbands. But, Piro said, Otakon “is not a babysitting service.”

“We want to do everything we can to keep our attendees safe,” she said. “But there’s only so much you can do. . . . There are definitely sketchy people out there. They could be at the mall. They could be at McDonald’s. This is still the real world.”

* * *

Anime is a broad medium that ranges from the purely innocent to the pornographic. Some of it fetishizes young girls.

The Alper arrest and conviction became a hot topic among anime fans, some of whom fear being further stigmatized. (Many of them already think that other people consider them geeks who live in their parents’ basements.)

“Leave it to the sickos to make the rest of us older guys that go to cons feel like eyeballs will be watching us double now,” one poster wrote on the Anime News Network forum. “I already have issues with going to cons and being the odd man out, and this guy has to make it just that much harder.”

Said Katsucon’s Diederichs: “It does propagate a terrible stereotype that some people have about male fans that attend anime conventions.”

But an uncomfortable undercurrent is obvious. Just consider the visual snapshot of attendees at any anime convention now.

“You get hundreds and hundreds of young girls in skimpy costumes . . . and then you have older male anime fans,” Diederichs said. “The juxtaposition of the two may not look entirely wholesome.

“I myself feel a little uncomfortable sometimes [at Katsucon] when I have to say to the third girl in a weekend who is wearing something too revealing, ‘Go back to your room and get more dressed.’ ”

At Otakon, there were people “cosplaying” — or costume-playing — characters from their favorite anime series and video games and sci-fi films. There were pirates and vampires and superheroes, along with a Rubik’s Cube and a My Little Pony.

Everywhere you looked, there were older girls dressed as little girls and little girls dressed as littler girls — and grown men taking photos of all of them. Sometimes, the men asked for hugs, too.

“There’s a little bit of perviness,” said Jamie Blanco, who was cosplaying a teenager from the hit anime series “Bleach.” (In real life, she’s in her 20s and the morning-drive producer for Federal News Radio.) The majority of people who attend anime conventions, she said, are there “because of a pure love” of the art form, its characters and stories. “But there are definitely a small percentage who come here to hug up on some of the younger girls — and younger boys.”

At the trade bazaar in the bowels of the Convention Center, one could buy all the too-short schoolgirl outfits one would ever need. Also on offer: hentai, or pornographic comics, some of which leaned Lolita.

* * *

In 1994, before anime moved in from the outer edges of fringe culture in the United States, David Stoliker attended the first Otakon. He has turned out every year since. He is 43 now, a physical therapist from Long Island. His summary of the demographic shift at Otakon: “There are definitely people who can wear skimpier costumes a little better.”

But don’t take that the wrong way, he said. Most of what happens at Otakon “isn’t prurient. It’s certainly not criminal.” An encounter like the one between a registered sex offender and a 13-year-old at Katsucon, he said, “can happen anywhere. People tend to draw attention to it when it happens in an unusual environment.”

Outside the Convention Center, cosplayers in animal outfits and gas masks and wigs generated triple takes (and occasional heckles) from drivers on Pratt Street. For Otakon attendees, it was business as usual.

A man dressed in a “Pedobear” costume was there, portraying the creepy satirical mascot that first emerged on the Internet as a way to mock inappropriate behavior in anime Web forums. Pedobears are regulars at anime cons, where many attendees appear to be in on the joke.

“Everybody loves Pedobear,” Travon Smith, the 20-year-old Baltimore man inside the sweltering teddy-bear suit, said — while assuring anyone within earshot that he is not, in fact, a pedophile. He also is not endorsed by Otakon but came to the conference as a paid attendee. “It’s all a joke,” he said. “Just people having fun.”

In his costume, Smith posed for photos and shook hands. People laughed. A young girl hugged Pedobear.