Kamen Rider Build Episode 16

Gentoku’s words brought doubt to Sento’s ears! The fact that Sento is actually the demonic scientist himself has really brought him down. He keeps repeating to himself that he was the one who experimented on humans and created the monsters called Smash. Sento starts to fill with guilt. However, Ryuga speaks his mind. He knows he cannot continue to fight alongside him if he knows he was the scientist behind the technology that killed his girlfriend. Ryuga summons Sento to him by saying… “Fight me”… (Source: kamenrider.fandom)