You don’t know much about yourself, except that you’re an attractive young career woman living in San Francisco. You’re standing in front of your burning apartment, where five hunky men who claim to be "soul collectors" have given you 10 days to live. One of them will accompany you until your death, to make sure you don’t run away. It’s up to you to choose between the muscle-bound Leo DeVille, raven-haired Blake Graystone, professorial Raphael Moreau, fresh-faced Kieran Van der Belt, or his ruthless older brother, Xavier.

You choose Xavier because of his intriguing, two-dimensional blue eyes, and eagerly click through to read the rest of the story.

That’ll be $3.99.

This is "My Killer Romance," a romance novel distilled into a Choose Your Own Adventure-style app. It’s a typical example of a "romance simulation" or romance sim, a genre that has been popular in Japan but is just emerging in the US.

Voltage, the Tokyo-based publisher that dominates the romance sim market, has struck gold with the formula. Other romance sims charge players to purchase virtual goods, but Voltage hooks the player with potboiler story lines, stopping at cliffhangers and requiring a payment to go on.

"You won’t purchase clothes or coins or whatnot," says Shino Imao, spokesperson for Voltage. "It’s more like you sit down and immerse yourself in a love story."

A love story that often ends up with cartoon men taking their shirts off, that is. Voltage titles are pretty tame, but the erotic, escapist themes parallel those found in romance novels. Voltage’s romance sims are similar to "dating sims" in which you can create a virtual girlfriend or boyfriend and then interact with it as if you’re dating (or have it talk so dirty to you that it gets banned from the App Store). But unlike dating sims, romance sims are exclusively marketed to women.

Romance sims are uniquely addictive, however, and they’ve monetized extremely well in Japan. Voltage just became the sixth-highest-grossing app maker on the Google Play store, according to analytics from App Annie, placing it just behind comics publisher comiXology. (That ranking excludes games, which are in another category.) GREE, another Japanese app that serves as a platform for romance sims, placed third on that list. Voltage actually does even more sales on iOS than Android, the company says, but has not cracked the top ranks there.

The company adds extra characters and story lines to each game every other week, Imao told The Verge, another way it keeps players coming back for more. Indeed, it’s easy to find hardcore Voltage fans gathering on Tumblr, Twitter, and in forums to giggle over their favorite characters and talk about upcoming story lines. "OMFG!! Xavier is soooo hot!! I can’t stop drooling," one Tumblr user wrote. Others players post lists of the choices they made — "hint about your feelings," "brush the hair away from his face" — with each character.

Voltage released three highly anticipated characters last month, which is possibly why the company’s revenues were so high. "We have very strong followers," Imao says.

Voltage has six US titles, with two more coming out by November (each game takes about six months to make). In "To Love & Protect," you play the president’s daughter, attended by a sexy bodyguard. In "My Lover is a Thief," you’re adopted by a band of crooks. "I actually feel like I'm falling in love with the guys! I can't even put my phone down," one satisfied iPhone user wrote on iTunes.

But even though the company has been making US-targeted sims for a year, most of the money still comes from Japan, says Marcos Sanchez, vice president of global communications at App Annie. "That type of app really plays well in Japanese culture," he says.

So will romance sims be taking over in the English-speaking world next? Imao has high hopes for two soon-to-be-released games, including one set in 1920s Chicago and another one that’s top secret. "We are really really focused on story line as well as fashion, because that’s what women want," she says. "We have fabulous fashion, and pretty boys as well."