On Saturday, Tatayanna Mitchell, 21, will fly from Michigan to Newark, N.J., to spend two days with a boy she met on TikTok.

Ms. Mitchell’s TikTok videos have become a fixture of the app’s For You page over the last month. She traffics in a format known as the “duet,” a reaction or response video that plays alongside another user’s content. And Ms. Mitchell’s humorous duets have become an art form.

Posting as @thereal_tati, she has virtually hung out poolside with Snarky Marky, another TikTok creator; shown off her vocal abilities in a music studio; and defended a friend who was getting bullied.

But by far, Ms. Mitchell’s most popular duets have been with TikTok star Devin Caherly, 19.

Mr. Caherly creates POV, or point-of-view, TikToks, in which he invents scenes and acts out specific characters within them. After he posts his one-sided skits, his followers, including Ms. Mitchell, act out another character as a duet. In one video, Ms. Mitchell and Mr. Caherly pretend to play a game of spin the bottle.

“I started to make something like a story line with me and him,” Ms. Mitchell said. She began duetting streams of his videos until he finally noticed her and began to play along. Suddenly, a romantic plot emerged. “If y’all don’t actually get married!” one user commented, many others began responding to their duets with “ship.”

Less than a month after she joined the app, Ms. Mitchell is at more than 2 million TikTok followers. She also started a YouTube channel. Mr. Caherly has also seen his star rise.

“People started saying, ‘you guys should date,’ and they started making hashtags and marriage videos,” Ms. Mitchell said. The hashtag #Tevin began spreading (a combination of Tati, as she’s known on the app, and Devin).

On June 25, Mr. Caherly posted a video in which he said that if it got a million likes, he would fly Ms. Mitchell out to New Jersey so that they could meet and collaborate in person.

It was exactly what millions of fans had been clamoring for. The video got the requisite million likes in a matter of hours, and four days later, Ms. Mitchell had booked her trip east.

Since then, the excitement has been building. Fans have been commenting about theories on how their first meeting will go and what videos they’d like to see them create together. Ms. Mitchell said she will be staying in a hotel during her time in New Jersey and unfortunately will not be able to host a meet-up as so many fans have asked for, because of the coronavirus. “We don’t want to put anyone in harm’s way, so we’ll probably do some FaceTime calls,” she said.

In anticipation of her arrival, Mr. Caherly has posted skits on his TikTok where he jokes about picking her up from the airport and going engagement ring shopping. But both Mr. Caherly and Ms. Mitchell say they’re just friends. The romance is a POV plot, and the fans are in on the joke.

“We have similar personalities, and we can explain the whole story line,” Mr. Caherly said. “It hasn’t really been done before, what me and Tati have been doing on TikTok. I think people are fascinated with how we both feed off each other. I wouldn’t call it a movie, but it’s a whole story we built across TikTok.”

Jacob Pace, the founder of Flighthouse, a media brand on TikTok, said that story lines like this can be very compelling. “She kind of made this a meme out of duetting with someone,” he said of Ms. Mitchell. And duets can be a powerful vehicle for growth. A large part of the way that TikTok’s most-followed influencer, Charli D’Amelio, initially amassed her millions of followers was by producing “duetable” content. As others posted duet reactions to her dance videos, her account became visible to more people.

Ms. Mitchell has employed a similar strategy. She duets other users, and people make duets to her content as well. An audio of her reading out the caption of a POV video saying “he has no lips! How will he get a kiss kiss?” has been used in more than 27,000 TikToks and became a meme.

TikTok fame has not affected Ms. Mitchell’s offline life very much. She works in a hospital and owns a dessert business. In addition to her personal account, Ms. Mitchell runs a food-themed TikTok account where videos, such as her recipe for dollar-store chicken fried rice, have also gained attention.

She dreams of becoming a full-time social media influencer, moving to Los Angeles and opening a dessert shop. The key, she said, is growing her following. “Hopefully I grow even more,” she said. “It’s rare to see Black creators on TikTok have over 10 million followers, I want to be one of those Black creators.”

In the meantime, she and Mr. Caherly need to keep people watching. Ms. Mitchell said the two have spent a lot of time on the phone and Zoom, strategizing how to make the most of their time together this weekend. They’re planning to drop custom “Tevin” merch and have been speaking to Bumble about a possible collaboration.

“A lot of people want us to kiss,” she said, laughing. “He has no lips. How will he get a kiss kiss?”