Two years ago, an online rant about the lack of day care in Japan went viral on social media and seemingly started a movement, prompting working mothers to stage demonstrations in which they demanded the government take them seriously and offer more child care.

Since then, there's been little progress: Though thousands of day care slots have been added, they've filled up quickly and long waiting lists remain, keeping women at home even if they want to go back to work. This illustrates the depth of the "returner mom" issue in Japan, which can ill afford to turn women away as it fights a persistent labor shortage and as Prime Minister Shinzo Abe pushes women-friendly workforce policies.

"There is more day care in Japan, for sure, but it's a cat-and-mouse game and the waiting lists are getting long," said Tsukiko Tsukahara, president of Kaleidist K.K., a Tokyo-based research and consulting firm.