The real Melody overlay code on a scripted fight. Check off the steps in order; with all six checked the board slides out and the cover over the key lifts. Pop Puretone and the key turns, and one button pops in for every Dirge your mana holds. Click any step to jump to it.
On the Mimic beta now: turn on Melody, flip its DIRGE switch, and the number beside it is how many Dirges your mana holds right now. The DISC key in the bottom right is up when Puretone is ready and down while it recharges. Full mana at 4,000 is five buttons; each one goes dark as its 800 mana is spent.