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.