When massive tsunami swept away entire towns in northeastern Japan five years ago, Taizo Son filled three shipping containers with emergency supplies and sent them to help the relief effort. Later, he bet almost $100 million of his own money on startups, seeking to transform everything from transportation and education to farming and medicine.

Now he’s ready to talk more about Mistletoe Inc., his project that’s aiming to be a combination of early-stage venture firm, incubator and entrepreneur-in-residence program focused on making an impact on society.

But Son, 43, isn’t just the founder of GungHo Online Entertainment Inc., the developer of Puzzle & Dragons, once the world’s best-selling smartphone title. He’s also the youngest brother of Masayoshi Son, chief executive officer of SoftBank Group Corp. Taizo is 15 years younger, worth about $12 billion less and generally keeps a lower profile. There are two other brothers in the Korean immigrant family from Kyushu. With similar hairlines, the family resemblance is unmistakable. So is the confidence.

“We aren’t deciding to do something because it’s profitable, or not do something if it isn’t,” Taizo Son said in an interview at Mistletoe’s new office in Tokyo’s Aoyama district. “What’s needed are like-minded people getting together to give shape to things.”

When he launched Mistletoe three years ago, Son sought to emulate Silicon Valley venture firm Andreessen Horowitz’s ability to draw on the knowledge of a network of experts, as well as Google’s ambitious backing of long-term projects.

One of Mistletoe’s startups is Zipline, whose drones will be used in Rwanda to deliver blood and medicine to rural hospitals. By flying and parachuting supplies, the fixed-wing machines can bypass the African country’s underdeveloped road network and get aid to those who need it in time. He’s also backing Zoox, a fully autonomous car, micro-satellite maker Astroscale and a toilet gadget that analyzes urine to detect diseases.

So far, Son has invested about ¥10 billion ($97 million) of his own money in 30 startups. That’s why he’s willing to wait 10 to 15 years — longer than most venture capitalists — for the bets to pay off. Proceeds from other investments — Taizo has also backed 500 Startups, Beyond Ventures, Grove Ventures and other funds — will help finance Mistletoe.

“Perhaps I’ve gotten old, reaching the age when you start to think about social responsibility,” he said, weighing in on Silicon Valley’s angst over whether the brightest minds in technology are being wasted on getting people to click on ads. “I’m interested in more direct solutions to problems.”

Son got his start in college by helping his brother get Yahoo Japan Corp. off the ground, and later made his mark with GungHo. When the company’s stock peaked in 2013, it was worth more than Mazda Motor Corp. and briefly made him a billionaire. He still owns at least 24 percent of the game developer, giving him a net worth of more than $720 million, based on data compiled by Bloomberg. Taizo Son remains on GungHo’s board, but is no longer an executive at the company. SoftBank once owned a 26 percent in GungHo, but announced in June that it would sell most of its holding.

As a major shareholder of SoftBank, the older Son is worth $12.5 billion, making him Japan’s second-richest man, according to the Bloomberg Billionaires Index. In July, SoftBank announced it would pay $32 billion to buy ARM Holdings PLC, as a bet on the future of the internet of things, an area that’s also important to Taizo and Mistletoe. While the brothers share a vision of solving humanity’s problems with technology, it’s also clear they’re going about it in different ways.

While SoftBank’s offices tend to be bland, like the rest of corporate Japan, Mistletoe is housed on two floors of natural wood and wicker furniture. Cables snake all over the place, a virtual-reality headset is nestled in a pile of controllers and a 3-D printer shares a desk with a bike helmet.

“I have my own way of doing things that is different from my brother’s and will eventually top him,” Taizo said. “Of course, he’s still way ahead.”

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