ピラピラ

adverb, adverb taking the 'to' particle, noun, noun or participle which takes 'suru'

fluttering; waving; small fluttering object

Describes thin, light objects like cloth or paper fluttering in the wind, or the objects themselves. Often used adverbially with と or as a する-verb.

• 旗はたが風かぜでピラピラとはためいている。

  The flag is fluttering in the wind.