The news highlights an increasing issue in Japan involving tenants leasing properties without proper contracts or permissions, essentially creating 'black-market' rentals. While the precise figures involved are still unclear, these unauthorized tenancies have been surfacing across various parts of Japan, with both tenants and landlords participating in such practices. Many are carried out secretly, bypassing legal norms and regulations to deal with housing shortage and high rental costs.

Housing and tenancy laws in Japan are typically strictly governed with authorities keeping a close watch to ensure compliant practices. However, these "yami-kosaku" or unauthorized tenancies reflect a growing issue in which tenants, landlords, and sometimes agents, in a bid to save on cost and paperwork, are flouting established rules leading to unregulated and unsafe rental practices.

In countries like US or EU, leases without proper contracts or permissions are also frowned upon and are considered unlawful due to the potential exploitation of both parties involved. Measures such as fines and lawsuits are in place to discourage such practices, including stricter enforcement of violation reporting systems.