In June 2016, WWE announced Vinci as one of the thirty-two participants in the Cruiserweight Classic tournament. He was selected to represent Italy during the tournament under the name Fabian Aichner. In the first round of the tournament, Aichner was eliminated by Jack Gallagher.
On June 5, 2017 it was announced that Aichner had signed a contract with WWE. On June 22, Aichner made his return at an NXT live event in a losing effort against Adrian Jaoude. He made his television debut on the September 27 episode of NXT, losing to Kassius Ohno. In 2018, Aichner began teaming with Marcel Barthel in NXT.
In early 2019, Aichner and Barthel began competing on the NXT UK brand in a stable with Alexander Wolfe and Walter, known as Imperium. On May 13, 2020, Barthel and Aichner defeated Matt Riddle and Timothy Thatcher (a substitute for Pete Dunne) to win the NXT Tag Team Championship. They would go on to successfully defend the titles against teams such as Oney Lorcan and Danny Burch, Breezango, and The Undisputed Era. On the August 26 episode of NXT, Imperium dropped the titles to Breezango, ending their reign at 105 days. They failed to regain the titles from them in a rematch on the September 16 episode of NXT.
On the special October 26, 2021 Halloween Havoc edition of NXT, Barthel and Aichner would defeat MSK for the tag titles for the second time. They would successfully defend their titles on the December 5 WarGames event, against Kyle O'Reilly and Von Wagner. On April 2, 2022 at NXT Stand and Deliver, Aichner and Barthel would lose the titles back to MSK in a triple threat tag team match also involving The Creed Brothers, ending their reign at 158 days. Aichner's final appearance as a member of Imperium was on the April 5 episode of NXT, when he and Barthel faced the Creed brothers in a losing effort. Aichner walked out on his partner Marcel Barthel, signaling the break up of the tag team. This was later proved true, especially after Imperium’s debut on Friday Night SmackDown, without Aichner.
On the May 24 episode of NXT, vignettes aired promoting the debut of Aichner repackaged as Giovanni Vinci. He re-debuted as a face on the June 14 episode of NXT, defeating Guru Raaj. On August 16, at the NXT Heatwave special, Vinci unsuccessfully challenged Carmelo Hayes for the NXT North American Championship.
On September 3, at Clash at the Castle, Vinci officially debuted on the main roster and realigned with Gunther and Ludwig Kaiser, with Kaiser announcing the reformation of Imperium. As part of the 2023 WWE Draft, Vinci and his Imperium teammates Gunther and Kaiser were drafted to the Raw brand.
On the April 22, 2024 episode of Raw, after Kaiser and Vinci lost to The New Day, Kaiser attacked Vinci, kicking the latter out of Imperium in the process. A week later on night two of the 2024 WWE Draft, Vinci was drafted to the SmackDown brand in the supplemental draft. On the August 9 edition of SmackDown, a vignette aired for Vinci’s return to the brand, reverting to his singles character from NXT 2.0 back in 2022. Vinci would eventually wrestle his return match for the brand on the September 6 SmackDown, losing to Apollo Crews in three seconds. Two weeks later, Vinci again lost to Crews and attacked Crews after the match.