The flanker has featured in four matches this season, and was named on the bench last weekend but wasn't injected into their clash with the Rebels.
Fakaosilea's contract was supposed to run until the end of the 2018 season, but the Brumbies agreed to release him.
He has struggled to make a consistent mark in his two seasons in Canberra, with injuries and a growing depth in the backrow limiting his chances.
The return of David Pocock to Canberra was always going to make the Canberra backrow a tough one to crack, while teenager Rob Valetini made a comeback from injury last weekend, along with Lachie McCaffrey, while Tom Cusack has gone from strength to strength in 2018.
Fakaosilea's destination in Japan is yet to be confirmed, but it is believed to be a side near Osaka.
The 22-year-old has played for the Aussie Sevens and spent two seasons with the Reds before heading to Canberra.