From the Super Mario Wiki
When the player decides to stop here, they will meet Petal Guy. His quest, Blossom of My Heart, involves getting his love letter to the person he's in love with. Although Petal Guy doesn't know her name, he describes her being a butterfly with a flower. That can only be Flutter from the 3rd floor of Mushroom Condo. The player should talk to Flutter. After the salutation, Petal Guy comes to read the poem to her himself. Flutter will be quite confused, and run away, but Petal Guy will reward the player anyway for helping him with the Gaddget, Bead Machine.