When Sudoku Met the Spirit of India

The Birth of my best selling Nintendo DS Game

You can design a product, even a strategy, but you can’t design who will fall in love with it.

The Spark on a Sudoku Grid

Mochizuki-san and I were on the train heading to a customer meeting. Between discussions about work, she pulled out Sudoku puzzle book and she said casually, “You Indians are really good at mathematics, aren’t you?”. "Not everyone" was my casual response, but, her comment made me pause. It wasn’t flattery; it was an observation about the way Indians approached numbers, patterns, and calculation. And in that brief moment, an idea sparked: what if Sudoku could go beyond placement? What if calculation itself could be woven into the puzzle?

That thought became the seed for Indo-shiki Keisan Puzzle: Indra. It wasn’t just about creating another puzzle, it was about blending the intuitive, rhythmic logic of Indian calculation methods arranged in a structure of Japanese problem-solving. On that train, I loosely planned a puzzle designed to teach, challenge, and engage in a new way. That single, offhand remark from Mochizuki-san helped me write a book on Vedic Mathematics in 2005.

The Classroom Dream That Flopped

At the start, I was chasing a pure idea "education through play". I shaped Vedic Mathematics book as a classroom tool: clean visuals, printable sheets, guided examples. Alongwith Shinyusha, the publisher, I approached schools, pitched it as “算数をもっとたのしく”, meaning "lets enjoy maths". The reactions were encouraging on the surface Japanese polite smiles, intrigued teachers, even a few enthusiastic demos. But when it came to actual orders, the result was silence. No purchase orders. I think it was around 600 books in 5 months.

In hindsight, I had built something teachers liked conceptually, but not something they could easily fit into their rigid curriculum.Kids didn’t demand it, schools didn’t budget for it, and I didn’t yet understand that in education, you rarely sell to the learner, you sell to the system.

That’s where marketing began to replace idealism. I realized passion alone wouldn’t carry this idea forward. The product had to find not just its purpose, but its tribe.

When Mothers Weren’t the Market

So the next chapter began, the pivot. The publisher Shinyusha, Game developement company, Gunho and me had a meeting and we decide to shift to digital and in a game format. Adapting the puzzle Indra for the Nintendo DS, which was gaining in popularity at the time. This wasn’t just a technical upgrade; it was a different positioning, the customer needs to ENJOY, HAVE FUN on the devide they use heavily!, not a book in the age of digital. Also we decided to shift the persona. THE MOMS! The new plan: reach mothers aged 35–45, the household influencers who decided what educational tools made it into the home.

We designed packaging that spoke to moms, calm colors, gentle promises of “learning through play,” the kind of tone that felt both smart and safe. We booked space in parenting magazines, crafted demos for family stores, and leaned into the image of a modern, nurturing mother investing in her child’s curiosity. It started selling, but were the kids really using them, adopting them and more importantly HAVING FUN?

When the Real Fans Were Seniors

The phone range on a workday afternoon when I was busy at the office. I still picked up, and the publisher on the other end chuckled: “Turns out our real audience isn’t kids, it’s seniors!”. Sales data confirmed it: the 60+ generation had quietly made Indra their favorite brain-training companion.The 60+ generation, seniors looking for a bit of mental gymnastics without the intimidation. Later, I even spotted some 70-year-olds on a train, calmly solving the DS version, this was unexpected, but it started making sense.

Many were already Sudoku enthusiasts, but Indra offered something new: calculation woven directly into the grid, rhythm and logic combined in a playful, almost meditative way. It wasn’t just a puzzle, it was a daily workout for the mind, fun enough to make them forget they were “training.”

This was serendipity at its finest. What began as a children’s educational game had accidentally found its true fans among seniors, eager for a brain-boosting challenge in the midst of Japan’s growing “mental fitness” trend. Suddenly, Indra wasn’t about teaching math to kids anymore. It was about giving older players joy, mental challenge, and that satisfying sense of accomplishment. This accidental insight of seniors quietly falling in love with an Indian-inspired calculation puzzle, became the key that unlocked Indra’s broader success. My takeaway, DO NOT OVERENGINEER CUSTOMER PERSONA, you never know who finds what value with what one creates.

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