After the forcible opening of Japan to the West in 1868, Japanese views of nanshoku began to be influenced by Western psychomedical views of homosexuality. On the one hand, this led to the pathologization of both homosexual desire and (more slowly and erratically) of the bishounen himself, whom Western theory positioned as an abnormal, feminized figure who must be firmly redirected on the path of proper masculinity lest he become a permanently perverted "invert". On the other hand, the Western location of homosexual desire within the weak, effeminate passive who fruitlessly attempts to seduce the masculine heterosexual male failed utterly to mesh with the Japanese image of the active, adult man who courts pretty passive youths. Shudo texts had generally supposed that the chigo or wakashu had no sexual desire for their lovers and did not enjoy being penetrated (although Edo-region prints often show the boy partner with an erection, and some show the nenja masturbating him), so during Japan's brief criminalization of homosexual anal sex per se, authorities were confused as to what to do with cases of men who offered themselves to other men as "bottom" outside of prostitution, a turn of events that Japanese legal codes had never contemplated.
Aside from the newly-discovered specter of the "invert", popular understanding of homosexuality became increasingly relegated to the realm of adolescence.
In Ogai Mori's semiautobiographical 1909 novel Vita Sexualis, the narrator separates the students at his boarding school into two types: the nanpa ("soft crowd") like himself, who are interested in fashion and women, and the koha ("rough crowd") who are sports fans, idolize military figures, and reject women as feminizing, instead pursuing pretty younger boys and terrorizing the other students in the process. Other Meiji writers describe similar phenomena under other names; the predatory gangs of older boys in the boarding-school dormitory, or the teenage juvenile delinquents who prowl the streets of Japan's cities, seeking out bishounen, preferably from upper-class families, to abduct and rape. Late 19th- and early 20th-century scandal-rags reported nearly weekly on sensationalized stories of attempted kidnappings, gang fights over the affections of boys, and other crimes laid at the feet of adolescent nanshoku-enthusiasts, whipping up a decades-long moral panic in the process. The koha, significantly, were always depicted as in their teens or early 20s; once a man hit adulthood he would naturally turn his attentions to women, as the more refined nanpa already did. And in this conceptualization, of course, the bishounen remains the blameless, socially approved and passive object of desire, as he was in former eras.
The koha panics faded by the 1920s, replaced in the minds of the moral guardians by crossdressed male prostitutes lurking in Tokyo's parks by night. The bishounen, at this point, is split: one part relegated to the "perverse press" and the red-light districts, one pure, virtuous and thoroughly disconnected from any taint of homosexuality.