The only Paraguayan to play in the A-League Men, Romero worked under Tony Popovic and alongside Jason Geria, Paul Izzo and Nishan Velupillay at Melbourne Victory, scoring twice in 10 games in 2023.
Romero, 26, also played alongside many Paraguay players at youth international level, and with and against others in the country's top domestic league.
He is good friends with midfielder Damian Bobadilla and played with Matias Galarza, who scored against Turkey, and several others.
And like many of his countrymen, Romero is flying high after a 10-man Paraguay beat Turkey 1-0, vanquishing memories of a 4-1 loss to the United States, to keep their hopes of reaching the knockout stages alive.
The equation is simple: if Australia win or draw in Santa Clara on Thursday (Friday AEST), they will finish second in Group D. If Paraguay win, they take the runner-up spot.
The loser would finish third and then hope to be one of eight best third-placed teams that will make the round of 32.
"Right now the spirits have risen again," Romero told AAP in an interview translated from Spanish.
"We were very sad and we were very afraid to lose again in that second game and go out of the World Cup very quickly.
"So this game (against Turkey) returned the hope of the people again. They saw the team we saw during the qualifying rounds for the World Cup again. So now people are hopeful again.
"And well, this game against Australia, for sure it's going to be a game of life or death.
"The one who wins goes on and the one who loses goes back to their country."
Paraguay are back on football's biggest stage for the first time since making the quarter-finals in 2010, eventually losing to champions Spain.
Romero and many of his compatriots thank coach Gustavo Alfaro for that.
"We love Alfaro because he brought back the essence of Paraguay. He gave us back what we had lost," Romero said.
"Before, we didn't have that fighting spirit, that desire to leave everything on the field. Every team beat us.
"And since he came back, we've beaten many teams we hadn't beaten in a long time - like Argentina, the world champions, and Brazil - and that's what we also saw against Turkey."
Paraguay will have their work cut out with star midfielder Miguel Almiron suspended - for covering his mouth in a confrontation with a Turkish opponent.
Romero believes Ramon Sosa or Gustavo Caballero, who have both struggled with injury this tournament, are the best options to replace Almiron if available.
Australia can expect a team that defends relentlessly, runs hard and tries to catch them on the counterattack, or as Romero puts it, "a very strong, very physical team that runs for all the balls and doesn't give up".
Romero, who watched Australia closely with his Sportivo Trinidense teammates during pre-season camp, sees the similarities between the fast, physical Socceroos and Paraguay and believes the clash will be a close one.
But he is backing La Albirroja to stand up and keep the good times rolling.
"It's very special because we are back in the World Cup again for the first time in 16 years," Romero said.
"We feel we can get to the quarterfinals.
"Then we have faith that we can get excited about going far in the World Cup because the team knows how to play decisive matches, difficult matches."
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