When Kouhei Maeda, a game director at Intelligent Systems, was in the midst of creating Fire Emblem Heroes, he laid out a plan. As the series’ debut on mobile, and a free-to-play title, Heroes needed a steady stream of content updates to keep players coming back. Maeda thought that if the team released a big update every month, that would be sufficient. But as soon as the game launched he realized it wouldn’t be near enough. “When we looked at the feedback we realized that people wanted more,” he explains. “So we really started kicking it into high gear so we could add more events and other content to the game.”

Fire Emblem Heroes is the second major mobile release from Nintendo, and a game that has quietly become a major success. Super Mario Run, the company’s debut mobile game, had a splashy on-stage reveal at an iPhone event featuring series creator Shigeru Miyamoto, and it went on to break a number of App Store download records. Heroes, on the other hand, was announced during a livestream event, tucked in between the reveals of a handful of other Fire Emblem games. But even as Mario Run has reached more players, thanks to its free-to-play structure and a steady stream of updates Heroes has proven to be the more enduring and lucrative release since it debuted in February.

The reasons for Heroes’ success likely come down to a handful of factors. For one thing, despite the shift to mobile and free-to-play, it still feels like a traditional Fire Emblem game, albeit one that’s been streamlined to better fit the platform. A big reason for this is that Heroes was developed at Intelligent Systems, the same studio that’s worked on Fire Emblem since its inception back in 1990. And that team wanted to ensure that the turn-based strategy that’s so core to Fire Emblem remained intact. “While it is mobile, and therefore you think of something that’s quick or easy to play, we really wanted to make sure that that strategy element was in there, and that it was really strong,” Maeda explains.

Another key element to Heroes’ ongoing appeal is the way the developers have responded to feedback. When the game first launched, for instance, many players complained about the stamina system, which limits how much you can play before having to either wait for it to refill or spend some money. “That was one of the things that we immediately acted upon and made changes to,” Shingo Matsushita, director on the game at Nintendo, explains. Subsequent updates addressed other early complaints by adding more characters and fleshing out the game’s story with new quests. These kinds of features are regularly addressed in detailed video updates.

Unlike a typical Fire Emblem release on a platform like the Nintendo 3DS, a mobile title like Heroes is an ongoing project. That’s been a new experience for a studio like Intelligent, which got its start on the original NES and Famicom. “Think of a normal Fire Emblem game as kind of being like a movie: you have a plan, you develop a script for it, and you know where it starts and where it ends,” Matsushita explains. “But Fire Emblem Heroes is kind of more like a TV series. Of course you have a vision at the beginning, but then you start getting some feedback, and based on that the TV series — or in this case game — can just keep getting better and better, because you’re reacting to the feedback from the players.”

Free-to-play can be a tough balancing act. It has the potential to creep into the game’s design, limiting fun in order to make it more profitable. That was part of the thinking behind Super Mario Run’s pricing: the game is free to download, and you can pay $9.99 to unlock the entire experience, with no additional purchases. Nintendo wanted this to be a more fair way of pricing, ensuring that parents didn’t have to worry about kids racking up a huge bill of in-app purchases. Fire Emblem Heroes goes in a different direction. Instead of a one-time fee, it features microtransactions that can be purchased with real money, and do everything from upgrade your castle to unlock new soldiers to add to your squad.

But despite being a more lucrative title than Mario Run, Fire Emblem Heroes is also more generous than many of its contemporaries, offering a surprising amount of in-game goods for free, so long as you play regularly. “The game is designed around the idea that free-to-play players, people who don’t purchase any orbs, will be able to play the game without any major difficulties,” says Maeda. “In no way do we make the game in a way that you have to pay in order to fully enjoy it.”

Much like Super Mario Run and upcoming mobile games like Animal Crossing, Fire Emblem Heroes is meant in part to expose an entirely new audience to Nintendo franchises. It’s something the company has already seen positive results from: the breakout success of Pokémon Go led to a significant boost in sales for the series on the Nintendo 3DS. Fire Emblem, meanwhile, is in a very active state, with multiple titles in the works for both the 3DS and the Switch. At the same time, Heroes is also a game that will likely have an influence on the future of the Fire Emblem series as a whole.

“I really think that our experience working on Fire Emblem Heroes will affect future Fire Emblem titles,” says Maeda. “One of the reasons for this, is that a lot of the staff that works on Fire Emblem Heroes are the same staff members that work on the core games in the Fire Emblem series. I think that they’ll be using this experience, as well as the feedback that we’re getting from players, and they’ll apply that to future titles.”