Darwin-born Rosas hopes to inspire another generation of Indigenous players, just as his grandmother Eileen Cummings helped him plot a path to the AFL stage.
Cummings is an Indigenous leader in the Northern Territory and a member of the Stolen Generations, forcibly removed from her mother in central Arnhem Land when she was four in the late 1940s.
Rosas Jnr, shy and soft-spoken, was most expressive when he paid tribute to his grandmother ahead of Sydney's annual Marn Grook clash against Collingwood on Friday.
The Marn Grook fixture is just one of many matches part of the fortnight-long Sir Doug Nicholls Round, a celebration of Indigenous culture and community.
"My grandmother's been a big part of my life. She's been my hero growing up," Rosas Jnr said on Thursday.
"She's been someone I can always talk to and be there for me.
"And even though I'm away from home a lot, she's always one call away or a message away.
"She's had a big impact on the Northern Territory. She plays a good role in that."
A Ngalakan and Remberrnga man, Rosas Jnr flew under the radar when he arrived at the Swans last year thanks to former Carlton spearhead Charlie Curnow's high-profile trade.
Featuring in all matches so far under coach Dean Cox, the 24-year-old announced himself with a career-best seven goals in the round-eight win against Melbourne.
The first thing Rosas Jnr, who played six seasons at Gold Coast, did was call his grandmother.
Rosas Jnr is also a grandson of AFL Indigenous Team of the Century member and Australian Football Hall of Famer Bill Dempsey.
"Yeah, I did (call her). She was just happy I'm out there playing AFL," Rosas Jnr said.
"I've been back home a few times playing footy up there with the Suns.
"There are a lot of heroes they (the kids) look up to. I'm just lucky to be one of them, lucky to be here.
"I hope they can find a path they choose and try to make something of themselves and be here.
"That's the main message I'm trying to get to them."
Rosas Jnr hopes to also add to Sydney's rich tradition of great players, including Adam Goodes, Micky O'Loughlin and Lance Franklin.
The team was greeted by past Indigenous players during Thursday's captain's run, including 2012 premiership player Lewis Jetta.
"I used to watch Jetta a lot when I was younger, Adam Goodes," Rosas Jnr said.
"It's definitely a different culture at the Swans from where I was.
"It's (Sir Doug Nicholls Round) a big thing - the percentage of Indigenous players getting drafted is getting pretty low, so it's just about keeping that connection."
Sydney are set to make at least three changes for Friday night, welcoming back Curnow (abdominal), Jai Serong (hamstring) and Tom McCartin (knee).
Meanwhile, Collingwood will be without veteran Scott Pendlebury (rested) and in-form ruckman Darcy Cameron (ankle).
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