Like their peers overseas, Japan's millennials aren't known for squirreling away their money. Kazuhisa Shibayama is trying to change that, one coin at a time.

The founder and chief executive officer of WealthNavi Inc., a startup backed by Japan's three biggest banks, is developing an app that encourages users to invest their spare change by putting aside a few yen each time they open their wallets.

The software works like this: When a customer buys something with their credit card or electronic money, it rounds up from the purchase price to the nearest ¥100 and collects that change. Once the balance reaches ¥500, the cash is channeled into an investment fund selected using the robo-adviser's algorithm-based technology.