ぴかぴか
ぴかぴか · pikapika · JLPT N2 · adverb
sparkle
💎 ぴか = a flash of light; doubled ぴかぴか = light flashing again and again, i.e. glitter
Doubling a sound-symbolic word (ぴか to ぴかぴか) marks repeated or continuous action. ぴか is the sound of a sudden flash, so the doubled form means light flashing over and over.