Molly Kate Kestner's voice, unfiltered and unexpected, has captured the world.

The 18-year-old Austin, Minnesota, high school senior is the big voice behind the YouTube hit "His Daughter," a fictional story about a young girl's journey as she heals from abuse.

"I might have not experienced it but I talked to people that had been through it but they didn't have the confidence to share it with other people," Kestner told ABC News today during a visit to Steinway & Sons showroom in New York City. "I was crying when I was writing it. … It's a really profound song."

Kestner said she wrote the song a year ago but posted it online Easter Sunday. "His Daughter" was written in just 15 minutes and recorded on a cracked iPhone while Kestner played on her grandmother's out-of-tune piano.

So far, the video has received more than 6 million views from 178 countries.

She even got an endorsement from superstar Jordin Sparks. Actor George Takei of "Star Trek" also shared it on his Facebook page.

"I wasn't thinking, 'Oh, this could be a huge hit,'" Kestner said. "It was another song I was recording. … That was my first take."

Kestner started playing the piano last year. She's written more than a dozen songs and has posted them online for friends and family along the way.

Kestner said she had no idea that "His Daughter" would strike a chord with so many.

Last week, she recorded "His Daughter" in the studio. As of now, she said she doesn't have a label or an agent.

"I've been taking it one day at a time," she told ABC News today. "I feel lucky."

ABC News' Paula Faris and Catherine Cole contributed to this story.

Molly Kate Kestner