Roberto Frois (ロベルト・フロイス Roberuto Furoisu) is a Christian missionary born to a Japanese mother and Spanish father. After being betrayed by his adoptive and demonically possessed father, Luís Fróis (who tried to use him as a genma experiment), as well as losing many close friends, Roberto is now on a mission of pure revenge.
Roberto's weapon of choice are his enchanced arms and fists, capable of numerous destructive boxing combinations. Roberto's gaunlets are based on the Christian archangel's, Raphael, Uriel and Michael, ordered from weakest gauntlet to strongest respectively. His alternate costume is William F. Guile from the Street Fighter series.
Roberto is first introduced when Soki and Tenkai meet him in a prison cell. At this point they try to help him, but Roberto replies in Spanish and attacks them. Later, he reappears when Soki confonts Mitsunari and Luis Frois and tries to kill Luis. However, both he and Soki fall through a trap door set by Mitsunari and have to fight off a corpse of former Genma Queen Hecuba. Afterward, Tenkai convinces Roberto to join the group using the Spanish tongue.
- The character's background is related to the Nanban trade period of Japanese history, which was the first contact between Japanese and Western cultures.