Fainga'anuku was formerly a wing or centre, but has demonstrated his versatility by playing on the side of the scrum for the Crusaders in the Super Rugby Pacific competition this year.
That flexibility has won him a recall to the All Blacks' 36-strong squad which will play Scotland on November 8, Wales on November 15 and England on November 22.
New Zealand are unbeaten in the Championship after beating France, Italy and Ireland at home in July.
The squad named by coach Dave Rennie includes two new caps and with nine players unavailable there are several recalls.
Prop Saula Ma'u and flyhalf Josh Jacomb are the players in the squad yet to play a Test. Back-rower Christian Lio-Willie returns for the first time this year, along with one-Test lock Jamie Hannah.
Centres Jordie Barrett, Quinn Tupaea and Anton Lienert-Brown, flyhalf Richie Mo'unga, back-rowers Ethan Blackadder and Anton Segner, hooker Asafo Aumua and winger Fehi Fineanganofo all return after missing New Zealand's most recent Test against Australia with injuries.
Winger Chay Fihaki is retained after making his debut against the Wallabies.
"This is a really strong squad we have selected," Rennie said.
"It's great to officially welcome George, Saula, Leicester, Christian, Jamie and Chay back into the squad. They have all shown fantastic form during the National Provincial Championship.
"Playing Scotland, Wales and England on consecutive weekends is a tough assignment. These are all proud rugby nations with passionate home crowds. We will embrace the challenge and the opportunity to build on our Bledisloe Cup performances."
Unavailable with injuries or for personal reasons were Ardie Savea, Samisoni Taukei'aho, Shannon Frizell, Tyrel Lomax, Leroy Carter, Ruben Love, Luke Jacobson, Caleb Clarke, Ollie Norris and Simon Parker.
ALL BLACKS SQUAD:
Forwards: Ethan Blackadder, George Bell, Scott Barrett, George Bower, Ethan de Groot, Leicester Fainga'anuku, Jamie Hannah, Fabian Holland, Peter Lakai, Saula Ma'u, Fletcher Newell, Xavier Numia, Anton Segner, Codie Taylor, Pasilio Tosi, Tupou Vaa'i, Josh Lord, Christian Lio-Willie, Wallace Sititi.
Backs: Jordie Barrett, Beauden Barrett, Chay Fihaki, Fehi Fineanganofo, Rieko Ioane, Anton Lienert-Brown, Damian McKenzie, Richie Mo'unga, Josh Moorby, Kyle Preston, Cam Roigard, Cortez Ratima, Timoci Tavatavanawai, Quinn Tupaea, Will Jordan, Josh Jacomb.
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