The 22-year-old, who can operate in a number of positions, joins the club from Nadroga in the Digicel Cup in his home nation.
"He adds another edge to our backline and gives us depth in key positions that we didn't have last season," team manager Andy Lloyd told reporters at a press conference.
"Although he's played sevens rugby he isn't just a stereotypical sidestepping sevens player, he has physicality and power which makes him a very dangerous player.
"He's versatile and positionally he has good awareness of what is happening around him. As with the other signings we've made this summer, Aisea may be under the radar, but we have worked hard to identify players who will bring something different to the mix."
Natoga has been capped five times by his country.