The Angel Flute can be obtained in Memoria during Disc 4. Just after defeating Maliris (the snake looking thing with 6 hands and 6 swords), there is a room with numerous pillars and a pink skyline in the background. It is on the small stone platform in the center, just to the left of the gravestone. You will see the ! field icon when you are in the right spot. The Angel Flute is Eiko's Ultimate weapon.