An anonymous businessman has signed Rola Misaki, 22, who appears under the screen name Rola Takizawa, on a 15-year 'exclusive service' contract.
The mystery man is said to work in the entertainment industry.
Sources quoted in Asian media said the man's "property holdings alone are worth several hundred million dollars".
"At events, his behaviour includes giving million-dollar tips to participants," said the source.
The pair are reported to have recently attended an event together in Beijing with him wearing a mask to hide his identity.
Ms Misaki, who is half-Japanese and half-Russian, appeared close to her new boss, holding hands with him on stage.
She made her debut in the adult video industry in 2012. After failing to find many fans in Japanese went on to become a hit in China.
According to Chinese journalist Eiji Miyagi: "If you ask someone to name a popular Japanese person, the response would probably be the name of this actress.
"It is viewed as a way for the younger generation to let off steam."
She now has over 4.8 million followers on Sina Weibo, the Chinese equivalent of Twitter.
Fans there have now gone online to mourn the loss of the porn star.
One, GuangY, wrote: "Nooo! She can't leave us like this."
Another, Mai86, wrote: "She's one of the best, a natural. I can't believe she's gone off with this man."
While Bao Hung posted: "It's a sad day for us fans. Come back to us after 15 years. We'll still be here."
