…with a 3D rendering of diamonds
(E ni kaita mochi; “A rice cake drawn in a picture”)
Something appealing that doesn’t actually do any good. Pie in the sky, to substitute a Western food. No matter how well-drawn and delicious-looking a mochi cake in a picture may be, you can’t actually derive any sustenance from it. Alternately, something that exists only as an idea or plan rather than in reality.
This idiomatic expression comprises a single noun phrase. At the end we find the primary noun, 餅 (mochi), a category of sticky sweet cakes made of white rice that’s been pounded into a single glutinous mass. The noun is modified by the verb 描く (kaku, although in other contexts it can be read egaku), “to draw a picture,” in plain past tense form. The particle に (ni) places the drawing of the mochi in the noun 絵 (e), “picture.”
The “picture” (絵) may be expressed with the character 画 instead, without any change in meaning or pronunciation. In turn, this allows the whole phrase to be condensed down to the two-character compound 画餅 (gabei). Another variant specifies the rice cake as 牡丹餅 (botamochi), in which the rice ball is surrounded in sweet red bean paste.
This saying apparently originates in the 通俗編 (Tōng sú biān, or Tsuuzokuhen in Japanese), which we’ve seen before.
(“Osore irimasu ga, ani ni okane wo kasanaide kudasai. Warugi wa nai ndesu ga, ano keikaku wa mina e ni kaita mochi ni suginai mono bakari desu yo.”)
[“I’m really sorry, but please don’t lend my brother money. His intentions aren’t bad, but his plans never amount to more than pretty ideas without any substance.”]