The Cronulla prop, whose side hosts the Tigers on Sunday, is good friends with Fainu through his older brother Manase, the pair having played together before the ex-Manly hooker was jailed in 2022.
The Tigers have long hoped Manase's younger brothers - Samuela, Latu and Sione are all named to face the Sharks - would turn into legitimate NRL stars.
Samuela, 22, has been a slow burn but 56 games into his NRL career, Fonua-Blake says the rampaging back-rower is starting to realise his potential as one of the competition's most threatening edge forwards.
"I played with Samuela's older brother and he was always at my house hanging out and playing ping pong," Fonua-Blake said.
"I've known him for a long time and I'm proud of him, Sione and Latu.
"Watching those guys grow up and make it to the big stage they're obviously not just being happy with being on the big stage, they're taking it that step further.
"I feel like Samuela is probably one of the in-form back-rowers in the comp.
"He's comfortable in his own skin and not worried about what other people think of him or anything like that, he's content with what he's doing."
There is a good chance Fonua-Blake could line up alongside Samuela Fainu for Tonga at the World Cup later this year.
Fainu has yet to play Test rugby league but his two tries and three try assists across the Tigers' 5-2 start are sure to pique the interest of Tongan coach Kristian Woolf.
"A few boys like myself are getting a bit older and my time to bow out might come soon, but at least we can say that the nation's in good hands," Fonua-Blake said.
The 30-year-old Sharks prop is desperate for his side (3-4) to show a reaction and rediscover their defensive steel against a Tigers outfit that will be without Jahream Bula and Api Koroisau.
Sharks coach Craig Fitzgibbon claimed his team, who has conceded 80 points across the last two weeks in losses to the Sydney Roosters and North Queensland, needed to fix their attitude.
"A few of us sort of limped into that (Cowboys) game thinking we've got a good team on paper and that it's just going to happen for us," Fonua-Blake said.
"It's definitely a little attitude check and we need to rectify it this weekend.
"If we keep going the way we are then finals footy is going to get out of our grasp."
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