Phantom Siita successfully holds their first live "Heine" at Nippon Budokan only half a year after their indie debut and launches a world tour at an unprecedented speed. After returning to Japan, they hold their first Japan tour "1st JAPAN TOUR Flame Medusa" in summer 2025, visiting Tokyo, Osaka, and Aichi, and reaching the final at Toyosu PIT. From July 2026, they are scheduled to hold their first Zepp tour across five cities nationwide, with tickets already sold out. Continuing their rapid rise, Phantom Siita releases their second single that defines the group's symbol. The lead track "Horror Queen" is written, composed, and arranged by Vocaloid producer Teniwoha, who also worked on one of their representative songs "Zokuzoku." This track embodies the evolved Phantom Siita since "Zokuzoku" and presents their reign as a queen under the concept of "horror," making it a culmination of the group. The coupling track is "Mo-ii Kai?" written by Hitoshizuku_Yamasankakkei, and it serves as the ending theme for the TV anime "The Strongest Job Is Apparently Not a Hero or a Sage, but an Appraiser (Provisional)" in the April 2026 season. The Limited Edition Blu-ray includes special stage performance footage of "Horror Queen" and "Mo-ii Kai?" along with the music video making-of footage Extended Version. Comes in a tall-size digipak specification.