Note that all adjectives that end with い belong to i-adjectives. For instance, きれい, ゆかい, よけい, ささい, 不似合い, 嫌い are all na-adjectives. (The first four are Chinese origin compound words (綺麗, 愉快, 余計, 些細), and the last two are derived from verbs 似合う and 嫌う, respectively.) My two cents.