To obtain the A Melody Sustained standard quest in Xenoblade Chronicles 3, interact with the lute on the western side of the Argan Cathedral Ruins.
For this quest, you’ll need to bring the lute to Miguel in Colony 9. He’ll task you with gathering guts from a monster at the Old Legre-Bhaja Battlefront in Aurora Shelf which is just northwest of the Diablada Cliffs. You’ll find this creature along the lake. Approaching it will begin a battle with the Lv. 47 Gigante Anlood. Take it down then Rex will do the honor of gathering the Rare Anlood Guts for you. Now that you have what you need, return to Miguel in Colony 9 to complete the quest. As a reward you’ll receive 4710 EXP, 3100 Gold, Gust Bracelet and Break Brooch.