[5] Yokoyama was scheduled to make his K-1 debut against Kazuma Kubo at K-1 WORLD GP 2018 JAPAN Featherweight Tournament on June 17, 2018.

[7] Yokoyama was scheduled to face Yuya at K-1 WORLD GP 2018 JAPAN Super Lightweight Tournament on November 3, 2018.

[9] Yokoyama was scheduled to face the future K-1 Lightweight champion Taio Asahisa at Krush 104 on August 31, 2019.

[12] Yokoyama was scheduled to face the former Krush Super Featherweight champion Yuma Saikyo at Krush.117 on September 26, 2020.

[16] Eleven days before the event, TETSU withdrew from the bout due to a torn meniscus, and was replaced by Yusuke.

He was scheduled to face Ryoga Matsumoto in the tournament quarterfinals, held at Krush 130 on October 31, 2021.

[19] Yokoyama won the fight by a second-round technical knockout, as he floored Matsumoto with a left hook at the 2:40 minute mark.

He managed to knock Yamamoto down twice by the midway point of the second round, forcing the referee to wave the fight off.

[23] After successfully rebounding from his loss to Nakajima, Yokoyama took part in the 2022 K-1 Super Featherweight World Grand Prix, held to crown a new champion after the previous titleholder Takeru Segawa vacated the belt.

[26] Yokoyama failed to advance further in the tournament however, as he lost by a first-round technical knockout to Hirotaka Asahisa, who knocked him down twice by the 0:37 minute mark of the opening round.

[29] Yokoyama faced the two-time Krush super featherweight title challenger Tatsuya Oiwa at K-1 World GP 2023 in Yokohama on June 3, 2023.

Both fighters suffered knockdowns in the second round: Oiwa being knocked down with a left straight and Yokoyama with a right hook.