Kamen Rider ZEZTZ: Case18: Shoot

In his dream, Baku, now a high school student, must protect his classmates—Nasuka and Kureha—from the Nightmare orchestrating a death game. As students fall, Kureha takes up a gun and challenges the Nightmare to battle. Seeing Baku intervene, Kureha murmurs, "...Seven." Why does Kureha know that name...!?