[Interview] How Japanese musician Grover turned his passion of ‘sound’ into a health-tech startup

JStories ー For over two decades, Yoshikazu Grover — better known simply as Grover — has been a familiar voice and face in Japan’s media industry. As a musician and radio personality, his career has been all about the power of sound.

Now, Grover is taking on a new role: tech entrepreneur.

He’s channeling his lifelong love of music into Fillgoo, a new health-tech app designed to measure how listening to music affects your mood and nervous system.

Grover has long felt that music does more than entertain — it can heal.

He kept wondering: What if technology could actually measure the positive feelings people experience after listening to certain songs?  Could this data be used to help people choose music that lifts their mood or helps them relax?

Over the past few years, he has developed Fillgoo (a playful take on “Feel Good”). The app uses a smartphone’s camera to detect changes in the user’s autonomic nervous system — specifically by measuring blood flow and pulse — before and after listening to a song.

The app’s prototype is already available for iOS users. Eventually, Grover hopes users will be able to share their data and even see song rankings based on how much they improve listeners’ moods or relaxation levels.

Grover traces his entrepreneurial journey back to a powerful experience a decade ago.

In 2014, he watched Alive Inside, a U.S. documentary showing how music therapy helped dementia patients rediscover memories and reconnect with loved ones.

“I saw people who seemed unresponsive or unable to communicate suddenly light up when they heard songs from their youth,” Grover recalls. “They would start smiling, hugging, even dancing. I was deeply moved by the sheer power of music to awaken the mind.”

The COVID-19 pandemic also reinforced Grover’s desire to build something new. As many in the entertainment industry faced uncertain futures, he reflected on how he could support his family — especially his two young daughters — if he could no longer rely on music or radio work.

Though Grover considers music his lifelong “best friend,” when it came to starting a company, he turned to another trusted companion: his older brother, Kaz.

Kaz, a seasoned finance professional based in the U.S., agreed to co-found Fillgoo. He now serves as the company’s CEO, while Grover focuses on marketing and promotion as chief marketing officer.

“Business was never my strong suit,” Grover laughs. “But when my brother said he saw real potential and offered to take this journey together, I thought — if he’s leading the way, I’m in.”

Family has always been central to Grover’s story. His Japanese mother, a classical violinist, once asked him to change the music in the car from classical to Latin because it reminded her too much of a strict childhood teacher. That moment reinforced for Grover how powerfully music triggers personal memories.

He also remembers advice from his late father, an Indian who studied in Japan, who often told him, “Be happy, always.”

That simple message inspired Grover to embrace what his father called “Happy Therapy”—a philosophy now embedded into Fillgoo’s mission.

Fillgoo remains in its early stages. The app is still a prototype, and the team is actively developing its business model and seeking partners.

One ambitious goal: helping Japan, a rapidly aging society, build a music-based wellness ecosystem. By promoting health through music, they hope to reduce healthcare costs — and perhaps even create a new revenue stream for songwriters and musicians.

Grover’s team is also exploring collaborations with wearable tech companies. While the current app uses a smartphone camera for measurements, future versions may gather data through smartwatches or rings.

This month, Grover will showcase Fillgoo at SusHi Tech Tokyo 2025, one of Japan’s biggest global startup events. He’ll personally introduce the app to visitors from around the world.

“It’s thrilling — and a bit nerve-wracking,” Grover says. “But I can’t wait to meet people, hear their reactions, and see how Fillgoo might help them in their own lives.”

Written by Toshi Maeda

Edited by Desiderio Luna

Top video: Giulia Righi (JStories)

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