"It's very addictive," Takeshita said.
"Even though the game characters aren't real, you start to develop feelings towards them."
That is the whole point, said Natsuko Asaki, a game producer at Cybird, which created the popular series Ikemen-a Japanese term for handsome guys.
"The story is most important, as well as the characters, and the twists and turns," Asaki said.
The Ikemen app has been downloaded some 15 million times since its launch about five years ago, and the firm has also released an English version.
Mirroring the smartphone boom, female-targeted virtual romance games have ballooned into a market worth about 15 billion yen ($135 million) annually in Japan, according to the Tokyo-based Yano Research Institute.
Some 80 percent of fans, including a growing number of married women, play just before bed, a Cybird survey found.
The games do not rely on complicated algorithms, but instead offer multiple choice scenarios that let players escape into a world where they create their own love story with digital hunks.