After the financial crisis, firms' funding rates no longer converged to LIBOR and came to differ with each firm's creditworthiness. Valuation adjustments for uncollateralized or partly collateralized trades are based on this firm-specific funding rate.
Consider a hypothetical example in which the funding spread is 0.50% a year and the positive part of the value is 60 million yen. The cost of funding it for one year is 300,000 yen (before discounting). The wider the spread, the larger FVA and MVA become.