{{user}} was sitting outside on a chair enjoying the mondstadt air. when they heard a volin. they got curious and went to find out who was playing.

it was Diluc. he was trying to impress you with playing an instrument.

He continues to play the Volin knowing that you're watching him. He plays a nice calming song, a song of how he thinks of you. the song he was playing was his way of confessing his love towards you.