A Chinese internet company that serves up homemade break-dancing videos, dishy news bites and goofy hashtag challenges has become one of the planet’s most richly valued start-ups, with a roughly $75 billion price tag. And it has big plans for storming phone screens across the rest of the globe, too.

You may not have heard of the company, Bytedance. You may never have used any of its breezy, colorful apps. But your nearest teenager is probably already obsessed with Musical.ly, the video-sharing platform that Bytedance bought for around $1 billion last year and folded into its own video service, TikTok.

“Frankly, it’s meaningless stuff,” said Dong Yaxin, 20, a college student in Beijing who says he is active every day on Douyin, the Chinese version of TikTok. Bytedance says that more than half a billion people worldwide use Douyin or TikTok at least once a month.

Cute pet videos. Lip-syncing to pop ear worms. Glossy digital effects …

A clip from @falcopunch on TikTok.

… and people who are very good at doing the robot.

A clip from @rezbkr on TikTok.

“There isn’t such a strong sense of purpose on Douyin,” Mr. Dong said. “That’s actually what’s so good about it.”

But even for a purveyor of fluff, crossing the tech world’s most treacherous divide will not be carefree. There are two major internets right now: China’s and the rest of the world’s. Beijing’s tough rules on content and operations have long made China difficult, even impossible, terrain for American internet companies.

Those rules have also largely penned in homegrown titans like Tencent, whose overseas expansion plans have been hamstrung by the unique demands of catering to China’s online population.

So far, Bytedance — which recently secured $3 billion in new funding from SoftBank and other heavyweight investors — has found a rare measure of success in both internets by doing things a little differently.

For one, it is making no pretense to be bridging the two digital realms.

Users of Douyin are entirely walled off from users of TikTok and vice versa; the better to manage the material that people in China can see. Beijing’s tightening controls have made these decidedly un-fun times to be in the business of fun.

Video game companies, celebrity gossip bloggers and live-streaming stars have all been through the wringer recently as the government works harder to stamp out cultural content that it deems unhealthy or unwholesome. The crackdown has not spared Bytedance — the authorities ordered the company’s joke-sharing app offline in April this year.

The company has also crossed borders with relative ease by focusing on light, affirming fare, and on attracting young — very young — users. But the Chinese Communist Party is not alone in having discovered a sordid side to Bytedance’s platforms.

Both before the company bought Musical.ly and since, horrified parents and others have reported finding adolescent users showing off suggestive dance moves on the app, mouthing lyrics about rough sex and worse. Police in Britain have investigated reports of adults propositioning children through Musical.ly.

Bytedance added new privacy settings and parental controls to TikTok in June. But if the company, which declined to comment for this article, cannot expand its ability to manage such issues at the same rapid clip at which it is drawing new users, its products could become the bane of many more parents and governments in many more countries.

Their children might not care.

Kang Sae-eun, 14, an eighth grader in Seoul, loves watching other young South Koreans on TikTok. There’s the girl who makes crazy faces, and the excellent dancer. There’s the cool girl with short hair — real “girl crush” material, she said.

They are funny and uninhibited, Sae-eun said. And best of all, they are regular kids like her.

“It is much harder for young people like elementary school students to become famous on the better-known platforms, like YouTube, Facebook or Instagram, all of which I also use,” she said.

Sae-eun said she didn’t realize that TikTok was made in China, which raises what might be the most interesting question about Bytedance: How did a company that is further democratizing self-expression come out of sternly undemocratic China in the first place?

Bytedance, which was founded in 2012, did not set out to dominate the market for bite-size videos. For many years, the company’s best-known product was not Douyin but a news aggregator called Jinri Toutiao, which uses machine learning to figure out what users like, then feeds them more of it.

In China, few media outlets command much loyalty among readers. That means an aggregator is a valuable and timesaving way to figure out what to read.

After a while, though, Beijing realized that an app that gave people exactly what they wanted ended up giving them a lot of not-very-wholesome stuff.

Last December, after China’s internet regulator accused Toutiao of spreading “pornographic” information, Bytedance halted updates to several sections of the app and removed or suspended hundreds of content creators. A few months later, Toutiao was temporarily removed from app stores for unspecified reasons. And Bytedance’s joke-sharing app, Neihan Duanzi, was shut down entirely.

In a lengthy letter of apology, the company’s founder and chief executive, Zhang Yiming, vowed to increase the number of employees moderating content to 10,000 from 6,000.

“The product went astray, and content appeared that did not accord with core socialist values,” Mr. Zhang wrote.

By then, Bytedance had another rising star in its stable.

Douyin was not even Bytedance’s first video app when it was released in 2016. But in the somewhat arbitrary, mildly mysterious way in which these things happen, it became huge.

The app is engineered for swift, maximal addictiveness.

Open Douyin or TikTok and you are plunged right into a video. Swipe up to get another, each refresh of the screen providing a dopamine jolt. The videos fill your phone display entirely, blocking the clock at the top and preventing you from seeing how many hours you have spent watching puppies and comedy skits and synchronized dancing.

Satsuki Hatashita, a 20-year-old college student in western Japan, has been hooked for months. She now knows not to use the app before taking a shower. “I wouldn’t be able to shower for a long time, until I finally stopped watching TikTok,” she said.

She, too, was surprised to learn that the app was Chinese.

People like Ms. Hatashita have given Bytedance confidence in its march overseas. The company has opened offices in Japan, Brazil, India, the United States and beyond.

Still, Chinese staff stationed in China oversee significant aspects of Bytedance’s international apps. They even produce some culturally specific content, such as push notifications suggesting videos to watch. The company is hiring speakers of more than a dozen languages, including Portuguese, Polish, Malay and Arabic, for positions in China, according to an online posting.

An episode this year points to the importance, for Bytedance, of having people on the ground in at least one area: government relations.

In July, the authorities in Indonesia temporarily blocked TikTok for hosting what they called “pornography, inappropriate content and blasphemy.” The Indonesian government had contacted TikTok’s Singapore office to give a few days’ warning. But it didn’t receive a response until after the app was shut down, Rudiantara, Indonesia’s minister of information, said in an interview.

Bytedance’s recent hires suggest that it wants to avoid similar incidents. Instagram’s head of public policy for the Asia-Pacific region, Helena Lersch, recently resigned to become Bytedance’s director for global public policy. Facebook’s public policy leads in Indonesia and Japan recently left to join Bytedance, too.

Before Douyin took off, China’s internet didn’t have a reigning social platform dedicated to short, easy-to-make videos. In the rest of the world’s internet, where Instagram, Snapchat and others are already popular, TikTok faces stiff competition.

For Tao Ni, a 25-year-old newspaper reporter in eastern China, Tencent’s messaging app WeChat has already become more of a tool for work than a fun way to kill time. Weibo, a popular Twitter-like platform, can be wearying. But not Douyin, Ms. Tao said.

It’s because each video is so short, she said, that she can end up spending hours on what amounts to channel-surfing. “Anything longer than 15 seconds, and I might start to feel tired.”