Re: bishounen and bonsai -- I think the metaphor can be sourced to Nanshoku okagami/The Great Mirror of Manly Love, is it (I had thought at first that it's from one of Saikaku's shorter homoerotic tales, but no). He means to say, I presume, that beautiful boys -- like bonsai -- shouldn't ever have to grow. A short lived and artificially stunted beauty, as per the pure ethics of Knabenliebe, samurai cool. Hah.
And Nosaka Akiyuki (not Tanizuki? if I recall correctly) did say once that the true bishounen should have something sinister about him. Hence, in retrospect, Yoshitsune and kabuki. And maybe, who will ever know, the Shinsengumi. It is interesting to note that Mishima was perhaps the first Japanese writer -- that I've read in English anyway -- to ever employ the now archetypal Evil Bishounen, in his novel Forbidden Colors (Kinjiki). Yuichi, the male protagonist, is the perfect beautiful boy. He is taught by an old misogynistic novelist how to feign emotions, how to pretend to love women, so he can destroy them.
And what of the translators of Thomas Mann, I ask you.