Pour ouvrir la porte, il faut faire une chaine d´échange d´objet.
Trading Chain:
1. You must talk to the Former Developer in Ritardando, either as Beat during
Chapter 5 or later as Allegretto once you can teleport back.
2. Talk to the Former Servant in Baroque City (near Lonesome Loco) who
will tell you more about Chord.
3. After defeating Rondo in Aria Temple, you get a Heart Pendant.
4. Once you can teleport around during Chapter 6 and 7, you can return to
Fort Fermata and enter a locked door to trade the Heart Pendant to Chord for
the Pot sitting near him.
5. Trade the Pot to a woman in Tenuto Village for some Goat Stew.
6. Trade the Goat Stew to the goatherd in Chorus Plains for a Coupon.
7. Trade the Coupon to the merchant in Hanon Hills for some Honey.
8. Take the Honey to the Magic Researcher in Baroque Castle.
9. Give photos of 20 different monsters to the Agogo Boy in Agogo Village
(since you can only carry 12 photos at a time, it will require at least 2
trips to bring enough) for Agogo Droppings.
10. The Magic Researcher will take the Agogo Droppings and give you the Odd
Candy after you spend the night at the Baroque Hotel.
11. Trade the Odd Candy to the merchant in Hanon Hills for a Glass Ball.
12. Take the Glass Ball to the priest in Baroque. He gives it back and tells
you to take it to the top of Aria Temple.
13. Take the Glass Ball to the top of Aria Temple, and examine the very back
of the top room where you fought Rondo. It will change into the Orb.
14. When you reach the top of Xylophone Tower in Chapter 7, place the Orb
in the slot at the back of the top room in Xylophone Tower. This leads
to a chest containing the Lion´s Chime, and also unlocks the 80-point
"Xylophone´s Treasure" achievement.