"Having aided the Cooper Gang with the Cooper Vault Job, the Panda King went back to China to live with his daughter, Jing King. He left in a hurry, apparently, as he left a small stash of his fireworks behind, which is sure to add a much needed attack boost for the Cooper Gang. It also seems to make Sly Cooper more resistant to damage for some reason as well..."
It is located on the roof of the weapons development facility. The code to access the vault is "1-2-3-4-5", and the passwords needed to access the treasure is "Flag", "Finish", and "Finale".
- Credit for coming up with this idea goes to El Grizz.