Outside of the monasteries, monks were considered to have a particular predilection for male prostitutes, which was the subject of much ribald humor. There is no evidence so far of religious opposition to homosexuality within Japan in non-Buddhist traditions. Tokugawa commentators felt free to illustrate kami engaging in anal sex with each other. During the Tokugawa period, some of the Shinto gods, especially Hachiman, Myoshin, Shinmei and Tenjin, "came to be seen as guardian deities of "nanshoku"" (male–male love). Tokugawa-era writer Ihara Saikaku joked that since there are no women for the first three generations in the genealogy of the gods found in the Nihon Shoki, the gods must have enjoyed homosexual relationships—which Saikaku argued was the real origin of "nanshoku". In contrast to the norms in religious circles, in the warrior (samurai) class it was customary for a boy in the "wakashū" age category to undergo training in the martial arts by apprenticing to a more experienced adult man. According to Furukawa, the relationship was based on the model of a typically older "nenja," paired with a typically younger "chigo". This practice, along with clerical pederasty, developed into the codified system of age-structured homosexuality known as "shudō", abbreviated from "wakashūdō", the "way ("Tao") of "wakashū"". The older partner, in the role of "nenja", would teach the "chigo" martial skills, warrior etiquette, and the samurai code of honor, while his desire to be a good role model for his "chigo" would lead him to behave more honorably himself; thus a "shudō" relationship was considered to have a "mutually ennobling effect". In addition, both parties were expected to be loyal unto death, and to assist the other both in feudal duties and in honor-driven obligations such as duels and vendettas. Although sex between the couple was expected to end when the boy came of age, the relationship would, ideally, develop into a lifelong bond of friendship. At the same time, sexual activity with women was not barred (for either party), and once the boy came of age, both were free to seek other "wakashū" lovers. Like later Edo same-sex practices, samurai "shudō" was strictly role-defined; the "nenja" was seen as the active, desiring, penetrative partner, while the younger, sexually receptive "wakashū" was considered to submit to the "nenja"'s attentions out of love, loyalty, and affection, rather than sexual desire"d"] Among the samurai class, adult men were (by definition) not permitted to take the "wakashū" role; only preadult boys (or, later, lower-class men) were considered legitimate targets of homosexual desire.