Japan's hot startup stocks have two things in common: They do business in areas that could be described as mundane, and they've pushed their founders into the league of the ultrawealthy. Take AI Inside Inc., which helps turn handwritten documents into electronic files. Or Rakus Co., whose goal is to help small and midsize enterprises with their bookkeeping and emailing services. Their shares have all more than doubled in the past year, enriching their founders and leading to talk of a burgeoning tech scene that's very different from Silicon Valley. While the companies are using technologies like artificial intelligence and cloud computing, they're applying them in less sexy ways.

Taku Toguchi knew he wanted a career in artificial intelligence as far back as when he was a teenager. Now 36, the college dropout and serial entrepreneur has joined the ranks of Japanese founders building fortunes in AI, thanks to a stock-market rally that turned his company into one of the nation's most richly valued. AI inside Inc., which went public in December and specializes in digitizing handwritten documents, has been among the biggest beneficiaries of surging investor optimism toward companies that use AI and other technologies to enable remote working. While some analysts have questioned whether the stock's almost ninefold gain is sustainable, AI inside has ambitious plans to expand outside Japan and into other business lines. "It feels like we're being hugely recognized," Toguchi said in an interview.