On the 8th, Seibu Lions announced that they will be holding the "Interleague Series 2026 - Black Lion's Fierce Charge -" at the Nippon Life Interleague Series 2026, which will be held at Belluna Dome from May 29th. For the nine games during the series, the team will wear the "Lions Black Mode Uniform," which is the first time in the team's history that the team will be using an all-black design.

In the world of the lion, the king of beasts, a jet-black mane is a symbol of absolute strength. The "Lions Black Mode Uniform" is designed to represent the mane of a lion that turns black as it continues to win battles. This jersey will be distributed to all attendees at the game against DeNA on May 30th, and Masayuki Kuwahara vowed through the team, "This year's interleague limited edition uniform is the first in the team's history to be entirely black, so I think it's a very cool and impactful design. I will play with all my might to fight through the interleague games with a performance worthy of this uniform and contribute to win."

In addition, the Hanasakitokuei High School Brass Band, the alma mater of Manaya Nishikawa and Dora 4 Keita Horikoshi players, will perform at the June 9 game against Hiroshima, and the Urawa Gakuin High School Brass Band, the alma mater of Yutaro Watanabe pitcher and Takuya Hiruma players, will perform on the 10th. On the 11th, the Waseda University Cheering Club, the alma mater of Kazunari Ishii player, will come for the first time to give a special cheer to the The Lions players.

Furthermore, singer Ikusaburo Yamazaki will be attending on the 9th. On that day, he will perform "Dare ga Tame" (For Whom), an anthem born from a conversation with former high school baseball players, during a mini-live performance before the game, and will also try his hand at throwing the ceremonial first pitch.