Luís Fróis, a Portuguese missionary and scientist, arrived in Japan during the Sengoku Period. He earned respect for his scientific work and was known for his kindness, particularly caring for orphans and adopting several children. He befriended figures like Nobunaga Oda. After Japan unified under Hideyoshi Toyotomi, Fróis was coerced by Mitsunari Ishida into researching the Genma, a demonic army allied with Hideyoshi.

His high status made him a target for possession by Rosencrantz, a Genma Triumvirate member. Under Rosencrantz's control, Fróis was forced to use his adopted children as test subjects for Genma experiments, implanting Dark Stones into them. These stones were part of a Genma plan to empower Hideyoshi and hasten the arrival of their god, Fortinbras. Despite the possession, Fróis sometimes struggled internally, resisting enough to implant prayer beads into his last surviving child, Roberto, granting him power to destroy Dark Stones.

Roberto initially believed Fróis willingly killed his siblings, but later learned the truth of the possession. Fróis's physical condition deteriorated under prolonged control, culminating in a transformation into a fly-like demonic form during the battle at Osaka Castle. His final act of resistance occurred at the Shimabara Research Facility, where he died alongside Rosencrantz during an explosion triggered by Claudius's death. This explosion destroyed the facility and ended Fróis's torment.

In the OVA adaptation "The Story," which compiles game cutscenes, Fróis's role is faithfully adapted, depicting his possession and forced actions under Rosencrantz. His internal struggle and inability to prevent his possessed body's actions are emphasized as a recurring theme.