Angry Birds Stella is the latest game in Finnish firm Rovio’s flappy franchise. Its pink heroine is joined by three female friends and a female arch-enemy; the game’s slogan is “best friends forever – most of the time”; and its aims include celebrating “female heroism”.

Angry Birds For Girls, then? Which is a controversial thought, given that Angry Birds has always appealed to both sexes, particularly among the children who are its most fervent fans.

Angry Birds Stella risks looking like an attempt to ghettoise female fans: Star Wars, Transformers, karting and RPGs over here for the boys, and something pinker and simpler for the girls over there.

Blanca Juti, Rovio’s chief marketing officer, makes the company’s case against this interpretation. “Just as I hope people don’t think Star Wars is for boys, I hope they don’t say this is just for girls,” she says.

“We want to challenge stereotypes, both on girls – that they only play easy games – and on boys, that they don’t like anything pink. We really want to challenge this, and there is already a bit of a movement around it.”

Juti says that when Rovio had a playable version of Angry Birds Stella on its stand at the recent Comic-Con convention “a lot of guys came to play”, and more convincingly, that just over 50% of people watching the game’s trailer on Facebook have been men.

“It does celebrate women: we have five female heroes and one male, and all the pigs... well, we don’t know what they are. But most importantly, we wanted to make a kick-ass game. I do think it will attract females as well. I hope it does. But it is not just for girls.”

You can look at Angry Birds Stella in two ways. A pinkified gaming-ghetto for girls sounds bad. A game with strong female heroes that’s played by lots of boys as well as girls sounds pretty progressive, though.

Having played it, I can testify that it’s not easier than previous Angry Birds games too. It will be interesting to see how reactions play out once the game is available, with cartoons, toys, merchandise and books to follow later in the year.

Boys and girls? There’s another sensitive topic when it comes to Angry Birds, which is how Rovio balances its appeal to children with the company’s desire to adopt the “free-to-play” business model that’s become so dominant in the mobile games world: giving the games away for free, then selling in-app purchases.

Angry Birds Stella has in-app purchases going up to £37.99 for a chest of 7,500 virtual coins. Par for the course in free-to-play games, but a potential eyebrow-raiser for parents whose children are playing – if not quite as big as the sight of a £69.99 kart in the Angry Birds Go! game last year.

“You can totally play the game without having to purchase stuff, but then on the other hand, if you want to purchase stuff, you can,” says Juti.

“That’s where the industry is going: people want to get the game for free, but somehow you need to be able to build the game. It’s an industry standard now. For us, free-to-play is a positive thing: it makes it extremely accessible to people around the world.”

The other big challenge for Rovio and Angry Birds in 2014 is staying relevant. Juti talks enthusiastically about its mainstream reach – “three to 103 year-olds: very few things in life, probably chocolate and Angry Birds, that have such wide appeal” – but there have been signs that its growth has stalled.

Rovio’s revenues rose by just 2.5% in 2013 to €156m (£128.4m), while stripping out its consumer products income revealed that the income from the Angry Birds games actually fell slightly year-on-year.

In its results for 2012, Rovio said it ended the year with 263m monthly active players, but the lack of a comparable figure in its 2013 results hinted that the number may have fallen.

Meanwhile, the company’s income pales next to that of rivals like Clash of Clans maker Supercell (£542m in 2013) and Candy Crush Saga publisher King (£1.1bn). Is Angry Birds falling back to earth? Unsurprisingly, Juti disagrees.

She cites a survey recently commissioned by Rovio in the US, Brazil, Korea and Finland that found an average “aided brand awareness” of 91%, rivalling well established brands like Disney and Lego.

That shows that people recognise Angry Birds, but it doesn’t necessarily prove that they love it and are still willing to spend money on it. That said, some of the other companies that Rovio has been compared to are encountering their own difficulties: witness evidence that Candy Crush fever (and spending) may have peaked.

“From the beginning, our aim has been to build a brand for 100 years, not 100 days. We have Stella coming in, Angry Birds Transformers coming out next month, another game soft-launched in Finland that’s coming soon too. So quite a lot of stuff coming this fall,” says Juti. “And we have a movie in the making too.”

The mystery soft-launched game may be RETRY, a Flappy Bird-esque action game that has been tested in Rovio’s home country since May, although it’s not an Angry Birds game.

Having dug around Apple’s App Store in Finland, there’s also a non-game app, ToonsTV by Rovio, which soft-launched there earlier this year but has yet to be released in the web. And ToonsTV might actually be Rovio’s best defence against claims of the company’s imminent decline.

Already available within other Angry Birds apps and on the web, ToonsTV has quietly become a Netflix-style TV network for kids, populated by Rovio’s own cartoons, but also shows from partners including Transformers and Fraggle Rock.

3bn video views since March 2013, and growing advertising from big brands, suggests ToonsTV is becoming an important second string for Rovio’s bow. “I would say to the sceptics, maybe hold on a little bit and play a few games,” says Juti.

“We have built this brand on many levels, through the games, toons, parks, products, and in different countries you can see that one or other is consumed more. Well, that’s fine.”