つつ

つつ attaches to the stem form of a verb (the ます-stem) to indicate that one action occurs while another action is taking place. It has a formal, literary nuance and is common in written Japanese, historical or formal contexts. It can be used to express two simultaneous activities, or to describe a progression of actions with a subtle sense of contrast or inevitability. It is more formal and less common in everyday speech, where ながら is often used as a natural substitute. Examples often feature careful, reflective or narrative tone and can pair a main action with another ongoing one.