Kamen Rider Build Episode 13

Sento’s expression suddenly changes after hearing the name that Nabeshima told him on the phone. Nabeshima tells him of a mastermind who would kill anyone for a million dollars. Sento locks himself in his basement without letting anyone know of his identity. Meanwhile, Ryuga confronts Blood Stalk who stole the Pandora Box. "If you find the Pandora Box, you hold a significant advantage over Hokuto and Seito." As for the several questions concerning his placement of the Pandora Box, Stalk lets them in on a big surprise... (Source: kamenrider.fandom)