He said recently in an interview that both Natsu and Lucy are the protagonist and that he looks at the two equally
Clearly a lie.....But...
Previously, Mashima had said that's Natsu was the protagonist/hero just like Haru was for Rave (versions of this were said a few times) and the original concept was based around Natsu.
Now I believe in the beginning of the fairy tail anime, Lucy's VA had more lines than Natsu's and it seems to follow her more because of narration and internal thoughts. With also things like the first movie and majority of the filler arcs literally being about Lucy.
Going back to Rave, the story could not have been without both Haru and Elle, even tho the story tended to lean toward more Haru-centered. Especially because we started the story with Haru. Plus we saw the story more from his point of view until the Hardner arc.
Now in FT, Lucy tells the story, plus we see inside her head more than Natsu. And like Elle, who was secretly extremely connected to the Rave stones (being Reisha and all), Lucy/her magic/Heartfilia women are connected to eclipse gate/Dragneel men/Igneel/dragons.
Now Erza as a female has more action sequence than Lucy but she is rarely connected to the main plot outside of the ToH arc and Irene shenanigans. In volume 9 Mashima was asked who is the main female.... Lucy or Erza and he said he would let the audience decide.
To me the reason why Mashima isn't clear for the Mc is because of the roles of these characters are blurred based on Mashima writing himself into the story.
Mashima was asked what character he was like or which he identified with..... He said he was more like Lucy but he would love to be Natsu or Erza.
When asked what inspired Natsu, he said his childhood.
So I believe these three characters represent 3 sides of Mashima and are all protagonist in their own right.
Lucy is the struggling writer who wants adventure and has to grow up and has to make money (rent being an early metaphor for Mashima's own bills) and a "noble loser" (like in the flare battle) who is a bit of a good ball klutz. She represents the present. In the beginning she was more light heated and fun which is what Mashima wanted the story to be like. Now she's more serious, emotional, with occasional forced humor.... Just like Mashima.
Natsu is the ADHD hero who wants to play video games and draw pictures for twitter. He is sporadic and cares deeply about his friends but also dreams of fighting Kubo and Oda. He represents Mashima's childhood/childish nature and dreams of wanting to grow up. Also he wants to impress his own father (a rather unattainable goal) who died before seeing Mashima become a successful artist.
Erza represents what Mashima's values... focused and determination. Like how he's always praised to be one of the most dedicated and hardest working mangakans. I think she represents Mashima's future of wanting to come out ahead. She also has the ability to stand up even after defeat even against unrealistic odds because he himself wishes to do this.
So you can look at the story as a balance of three characters that really should be one character.
These three characters also tend to have more favoritism shown to them by Mashima (Lucy having the least) and these characters tend to be called Marin Sues more (Erza and Natsu for battle moments with Lucy for nonbattle moments).
I really feel like I should get a reward for psycho-analyzing Mashima. It's a scary place to be for a female.
. I think when Hiro said who was his favorite character he said it depends on his mood. But we're talking MC. Erza ain't the damn MC of FT, where are people getting that? Now I'm about to find that interview where he said it was Lucy cause I'm interested now.
His interview in France clearly stated Lucy and Natsu both are the main characters
