Harry really liked Hagrid's gift of a flute in his first year, and soon, he was playing it almost every day near the Lake, or even in the common room, learning from books and attracting a small crowd of students, staff and even animals and creatures, his often melancholic notes brought many to tears, on his birthday before Second Year, he woke up to a more intricately carved one, that felt just right for him.
Harry's music brought forth emotions on those that heard it, and while many times it brought warmth and happiness, his life wasn't easy and the songs were often melancholic and sad, during Third Year they were even more hauntingly beautiful, a tune of longing for his parents' love, and even anger at their supposed traitor, though for some reason, the Dementors would avoid him when he was playing.
His friends tried to help him, and even Fawkes once or twice sang a beautiful duet song while Harry played his flute(said song reportedly made the Dementors get far away from the area, and brought comfort and hope to any who heard it), the melodies however, got even more melancholic after Harry's perceived failure to help Sirius be cleared of his charges and letting Pettigrew escape.
However, on his Fourth Year, after the foreign delegations arrived, Harry's songs became much happier; beautiful, warm melodies that attracted larger crowds and were often accompanied by birdsong, often, animals and magical creatures would get on the edge of the forest to hear it.
His friends and some of the staff were pretty sure it had everything to do with the beautiful girl in light blue that began to attend all Harry's "recitals" as they were being called, for in her presence, his songs made even flowers and plants bloom when he reached a crescendo, some swore even the weather cleared sometimes.
Hermione once caught Harry alone with said girl, who was dancing to his flute in a clearing, and she swore the trees swayed and lights danced around them while flowers bloomed in moments, even the wind seemed to swirl in harmony to the melody.