ki•mo•no

Pronunciation: (ku-mO'nu, -nO), [key] 
—n., 
—pl. -nos. 
1. a loose, wide-sleeved robe, fastened at the waist with a wide sash, characteristic of Japanese costume. 
2. a woman's loose dressing gown.

RULES : GAME :: soldier : _____(army)

The best answer is army. The relationship between the first pair of words, rules and game, is that of part to whole—the first word is a part or piece of the other. Therefore, the second pair of words must also have a part-to-whole relationship. A soldier is part of an army.