Kingdom is an anime adaptation of Yasuhisa Hara's manga series of the same name, which he wrote and drew. A fourth season was confirmed at the end of the third season's last episode, and it began on April 10, 2022. The ensemble reunited for a second time to repeat their roles. Suiren's "Rei -ray-" serves as the opening theme, while Haku's "Suiren (Dazzling)" serves as the closing theme.