On a recent afternoon, Yamashita Park in Yokohama's waterfront was teeming with visitors — from lovey-dovey young couples to picnicking families and foreign tourists taking selfies in front of the ocean liner Hikawamaru, a museum ship permanently moored at the park.

A short distance away, the city was also hosting the Tokyo International Conference on African Development, inviting a legion of foreign leaders as well as representatives of international organizations, civil society and the private sector.

Overshadowing this veneer of prosperity, however, are a population crisis and precarious fiscal health that figures show will start chipping away at Yokohama's growth in the not-so-distant future.