Rayleigh
Car redon est pas là, et CCC dit que ça peut dependre de quelques règles en jap'

Green Bull huh.
Well, "ushi" is pretty much guaranteed for the bull part, because all four precedents so far have used kunyomi for the animal, but midori for green would make it Midoriushi, which is kind of a mouthful. Akainu, Aokiji, and Fujitora all only have four mora (syllables, basically), and Kizaru only has three...
My prediction is Rokuushi. Some specific shade of green would also be possible (the way "fuji" is specifically the shade of purple in the wisteria flower), although I don't know any off the top of my head.
And Chinese zodiac theme is all but confirmed. If there happens to be an orange guy at some point, it's a good bet he'll be "snake"... (or pig, sheep, horse, rat, cat, or dragon, I guess).
