In August 2021, it was announced that Nishikubo, aged 18, would be joining J2 League club JEF United Chiba for the 2022 season.
He made his debut in a 2–1 league victory over FC Ryukyu in February 2022.
[1] He scored his first goal for the club later in the season in a 2–1 win over eventual league champions Albirex Niigata.
In January 2024, it was announced Nishikubo would be transferring to J1 League club Júbilo Iwata ahead of the 2024 season.
[3] This biographical article related to a Japanese association football defender born in the 2000s is a stub.