How do you get a lock on Rejjie Snow? Since first emerging through a YouTube portal six years ago, the Irish rapper’s biography has been as blurry as a half-remembered dream. In an era when your favourite artist’s memoirs can be pieced together one Instagram post at a time, Snow has forged a mystique more typically associated with Scottish aquatic monsters or Marvel superheroes.

Snow is no stranger to comic book mythology; his first rap moniker was Lecs Luther. His existence has felt off the grid. He swaps continents faster than he shuffles through vocal cadences. As I jump the tube on my way to his show at London’s O2 Forum in Kentish Town to speak to the rising star (formerly Alex Anyaegbunam), I scrawl a reminder in my notepad to ask what the hell country does he live in.

Snow first materialised on our monitors in 2011 with some sharp online music videos that showcased his dexterous flow and oblique writing style. He’s since spent time in England and the US, absorbing the company of rap stars such as Kendrick Lamar and Joey Bada$$, and parlaying his “next big thing” status into a healthy international fan base and a contract with influential hip-hop label 300 Entertainment. Right now, New York city is his most dependable address.

Snow's rise has been leisurely. In six years, he's put out a relatively small amount of music. This year, though, will see the release of his long-awaited debut album Dear Annie, an additional mixtape titled The Moon & You, plus a zine of poetry and street photography. His creative dam is bursting.

Going incognito

Walking into his dressing room, Snow greets me with a warm embrace, which is a relief. We’ve met before, but a few days previously he said he was contemplating not doing any interviews for this album cycle.

“It’s just where my head is at right now,” he says, leaning back on the sofa, dressed in a Lacoste tracksuit. “Just trying [to keep things] low-key. Incognito.”

In that respect, Snow takes after rap underground’s MF Doom. Hip-hop’s supreme super villain never appears under his stage name without sporting a metal mask. Snow has Doom’s name inked across his leg.

Like his hero, Snow's early tracks showcased dazzling technical proficiency, cramming syllable after syllable into his bars while keeping his flow laid-back and funky. He'd rap smooth as velvet over the kind of dusty jazz instrumentals his parents raised him on. Forthcoming album Dear Annie sports these influences, but it also works in some new styles, like the grim, unforgiving sounds of trap.

“I started with the music first, as opposed to the lyrics,” says Snow, his north Dublin accent unalloyed by his travels. “I wanted it to be more of a musical type of thing. The instruments were a bit more dramatic and weird, all different types of sounds. I think sonically for me that’s my most important thing.”

Dear Annie has been mooted for years. Duke Ellington once said: "I don't need time, I need a deadline." Last year, Snow got that time limit. When he was sent into a Los Angeles studio with renewed focus, the record finally crystallised.

“With the album, I just went in with that headspace in a timeframe. I had a date I had to deliver the album by and I had to make that. So that was hard initially but also fun to work on a deadline. I’d never done that before.”

In the studio, his unpuncturable aura refused to dissolve, even among his collaborators. "It's kind of hard to explain Rejjie Snow because you can't explain Rejjie Snow. That's what makes him great," says Rahki, a Kendrick Lamar collaborator and producer on Dear Annie. "You have to just be in his world and somehow get just try to get in his head to understand what's really going on. I've been in the studio with him every day for months, and I still don't know this kid. I still don't get him, but it's so intriguing."

Without a release date, Dear Annie remains in the chamber as the label waits for the optimum release moment. "To have that behind my name, it seems more seriously now," says Snow. "I feel like I'm a proper artist. You make these songs and you forget that it's all building to a point where I can make an album, it's great. I guess it's some kind of an achievement. It feels good."

Youth culture

Rejjie Snow is a proud Irishman. He's just not the Irishman the world might expect. The Drumcondra native rejects all paddywhackery. A couple of weeks after Enda Kenny pitched up at the door of Donald Trump with a bowlful of shamrock for the annual St Patrick's Day photo op, Snow dropped Flexin', a cement-tough trap track that targets at least one Irish stereotype for eradication. "Beg the boy to Riverdance," he raps menacingly. "I'm Irish, what you f**king mean?"

“You could say that. It’s more satirical to me, but you could say that,” says Snow when I ask if the song is about Irish typecasting. “[The stereotype] is not me, but at the end of the day, it is my culture, but it’s not that. I come from mates and friends and joyriding and stuff.”

Shot in Darndale, the video for Flexin' depicts the grittiest ripples of Dublin youth culture – all joyriding, dirt bikes and urban horse riding – albeit in a souped-up, music video kind of a way. Snow admits the clip isn't dead-on personal history ("I was more of an observer, never the one to get in trouble"). Still, he wanted to show the world a rarely seen side of his city.

"In America, they drink Lean [a cough syrup-based drug] and shit; [Flexin' is our] kind of thing, to me anyway. So it's about showing that to some degree, but not showing people [in] f**king leprechaun suits and shit. That makes no sense."

The video attracted some ire online as being slum tourism and even a little classist. Snow says he’s not too wounded by the words. “I’ve spoken to some [of the critics] about that. It’s funny, when you talk to people, it doesn’t change [their minds], but they understand it a bit more. I just can’t pay attention to that. I’m moving too quickly to even care as well. I don’t have to do this; I can do whatever I want. Anybody making artistic shit, I’m all for it.”

Operating in a world no Irishman has ever walked before, Snow is perhaps already the country’s most internationally recognisable rap artist (comedy rap pair the Rubberbandits, a very different two-headed beast, are well-known back home and in the UK, with the excellent Rusangano Family poised to make the international jump). He might be the rap game’s Conor McGregor: a star who has forged a global rep while cultivating a homegrown fan base partially attracted to his patriotism. Yet not everyone is sold, criticising the region-neutral nature of his work.

“In Dublin, I had a hard time anyway. Like a love-hate relationship with people,” Snow concedes. “Just being identifiable, that’s my main thing. No one gives a f**k, to me anyway, until you’ve reached some kind of level of success outside.”

Mellow and chilled

The O2 Forum in Kentish Town is a cavernous venue with an old-fashioned ballroom flavour. The crowd filtering in, though, is young. “He’s just really mellow, really chilled out,” says one teen fan queuing outside. She sports Rejjie’s name on her hand, decoratively drawn by a schoolmate in black biro.

After our interview, Snow leans his head back, hoping for a power nap to alleviate the fatigue that comes with touring. It’s one of a few attempts as the crowd filters in a few floors below and the support acts do their thing. But his slumber is broken by friends, reps and one big surprise: Snow’s dad and younger brother Josh, who show up unannounced.

Charles Anyaegbunam is one beaming father.

“People see that he’s carrying the Irish flag, proud of his origins,” he tells me happily, “but doing it on an international stage.” Speaking to him feels like a rare glimpse behind Alex’s impenetrable metallic curtain. The man of mystery temporarily unsheathed.

I wish Snow luck right before he springs out on stage. As the song 1992 rings out, the crowd sings the chorus right back with double the vigour. One punter stretches out the Irish Tricolour behind his shoulders. The night after, Snow will play Dublin's Ambassador venue. All roads, inevitably, lead home.

• Rejjie Snow's new mixtape The Moon & You is out May 19th. For more, see twitter.com/rejjiesnow