黒 kuro or 黒い kuroi means "black," and 剣 kenor 刀 katana refer to a sword. 黒い剣 kuroi ken, 黒い刀 kuroi katana, 黒の剣 kuro no ken, 黒の刀 kuro no katana, 黒剣 kuro ken or 黒刀 kuro katana could translate to "black sword."
The phrase 'black fire' would be translated as 黒い火 (kuroi hi) in Japanese.
Kuroneko.
Kuroi sasori.
Kurotsuki
kuro to shiro
Kuroi Ame
Kurogokegumo.
Kuro Kaze
kuroi inu
Kuroi ie/uchi.
'Black thunder' would be 黒い雷 (kuroi kaminari) in Japanese.
There are no plurals in Japanese. 黒い竜 = kuroi ryuu, or lit. black dragon. Hope this helps~