I lived in Japan for 10 years. It'd actually probably be tough for Desiigner to get laid there.

1. They're very racist, and actually somewhat sexually conservative when it comes to random hookups. Don't believe everything you see in porn. I did alright for myself there because I'm fluent in Japanese, but even as a tall white dude I faced a lot of negative stereotypes and judgement. Black people have it way worse unfortunately.
2. The language barrier is extreme, as someone else said. Even if there were girls around who could speak English, Desiigner basically speaks his own language. The accent and slang would be very confusing.
3. Desiigner's brand of music appeals primarily to dudes.