Earlier quoted context omitted.
On all the Japanese devices I've used, emoji input is a separate "keyboard" (or rather a different mode in the standard keyboard). Some Japanese keyboards will sometimes suggest emoji during input conversion (the normal kana->kanji step), but it's a somewhat haphazard way of inputting them, and it's often easier just use the dedicated emoji input. The reason seems fairly clear to me: many emoji encode nuances that do…
There is a separate emoji panel, but in my experience you tend to remember the name of the emoji used the most, and in 10-key mode it's pretty fast to type a 2 or 3 kana word. About the android phones, I was a bit surprised by the low quality of Japanese support. But I didn't try the ATOK keyboard nor the input available on Sony phones for instance, only the Google IME. To Apple's credit, they've been doing IME on th…
The main issue with conversion-based emoji seems to be discoverability.... Besides those reflecting basic concepts, there are tons of odd or intricate emoji that you'd never even imagine existed unless you saw them first; even once you know they exist, figuring out what input maps to them is at best a crap shoot (I've never found any way of getting the input system to tell you)....