He is signed to New Japan Pro-Wrestling (NJPW), where he is a member of The Mighty Don't Kneel stable and is IWGP Junior Heavyweight Tag Team Champion along with Robbie Eagles.

On August 24, 2021, Kosei made his in-ring debut match against Ryohei Oiwa, at Korakuen Hall, ending in a 10-minute time limit draw.

[4] On October 2, at AJPW Raising An Army Memorial Series, Fujita, Yuji Nagata, Yuto Nakashima, and Oiwa of AJPW fought against Kento Miyahara, Inoue, Yuma Anzai, and Takuya Nomura of Big Japan Pro-Wrestling, in an eight-man tag team match where the former won the match.

[9] On November 4, 2024, at Power Struggle, Fujita and Robbie Eagles won the Super Junior Tag League.

[10] On January 4, 2025, at Wrestle Kingdom 19, the duo won the IWGP Junior Heavyweight Tag Team Championship.