Fati's has made a stirring start to the season, scoring just two minutes into his full La Liga debut on a magical night when he hardly put a foot wrong in front of over 80,000 astonished Camp Nou fans who gave him a standing ovation as he left the field.
He was just seven years old when he first came to Spain and his startling talent meant he was invited to join Barcelona's prestigious youth academy 'La Masia' aged 10.
It was an incredible achievement for a boy from the impoverished West African nation that has never been known for football.
In Sao Paulo, his home neighbourhood in the rundown suburbs of capital Bissau, the children yell “Ansu Fati, Barca player!” as they run around on ochre soil, under the tropical trees.
Malam Romisio, who coached Fati as a child, told AFP how the boy used to play football wearing only socks or plastic sandals, easily dribbling the ball past bigger, stronger teammates.
When Fati made his debut with Barca's first team at the end of August, the coach switched his allegiance from Real Madrid.
“If he continues like this, he will be a great player,” he predicted.
In Guinea Bissau, which is one of the world's poorest and most fragile nations, Fati is a source of national pride.
Born on October 31, 2002, he lived in Bissau until he was six.
In the house where he grew up, Fati's uncle Djibi Fati shows photos of the footballer as a child, dressed in traditional clothes, recalling how others used to tease him for his love of bread and butter.
“Every time he came back from playing football, he would ask for it,” he recalls.
Family divided, reunited in Spain
When he was still very small, his father, Bori Fati, went to Portugal to look for work, later settling near Seville in southwestern Spain.
Bori picked olives, collected empty glasses in nightclubs and even helped build a high-speed rail track, recalls Amador Saavedra, who befriended him in Herrera, some 100 kilometres (60 miles) north of Malaga.
It was only when the Communist mayor of Marinaleda, a nearby town, hired Bori as a driver and helped him financially, that he managed to bring his young family over in 2009.
“It's a very beautiful story,” said Saavedra, 53.
Bori ended up training his young son at the Peloteros football school, which is free for thousands of children in Herrera and the surrounding towns.
Cheerful but quiet
When Fati arrived he quickly caused a sensation on the football pitch, said Jordi Figaroa Moreno, his first Spanish coach.
“He had a gift,” he told AFP. “The difference between him and his teammates was just huge, both technically and tactically. Among the youngsters, it's rare to find children who can play as a team, but he had everything.”
Jose Luis Perez Mena, who runs the Peloteros school, described Fati as “very spontaneous” and “very cheerful” as well as “extroverted, but very quiet”.
His stellar success “has not gone to his head”.
Within a year of arriving in Spain, Fati joined Sevilla. In 2012, at the age of 10, he was enrolled in Barcelona's youth system.
“Ansu was one of the youngest players ever to have entered La Masia,” said
Marc Serra, his first coach at Barcelona.
“From the day that he arrived he was different, the type of player who invents football.”
In August, the teenager became the youngest player to score for Barcelona in La Liga. This month he became the club's youngest player in a Champions League match.
Spain's national coach Robert Moreno described Fati's debut for Barcelona as “mind-blowing”. Barcelona coach Ernesto Valverde spoke of him as a “balanced boy” who is “at ease with himself”.
“We want him to learn to know himself, to know the first division, so he sees that it is hard and how much work and dedication it will take to succeed,” he said.
Speaking to Spain's Onda Cero radio last month, his proud father said he had taught Fati to “be respectful and happy with everyone”.
“Every day I tell him: 'This is your job: when you have the ball, turn towards the goal, don't look anywhere else, and just shoot.”
By AFP's Allen Yero Embalo with Laurence Boutreux in Herrera, Spain