Along with Fireworks In A Bottle, Fireworks For A Steal is a missable FF13: Lightning Returns side-quest that must be completed in Yusnaan, but only during the second main-quest in the area, named The Legend Of The Savior.
Fireworks For A Steal as well as its client will disappear if you continue the main-quest; however, since the side-quest and the said main-quest are connected, as a reward you will also receive a set of 7 fireworks.
This means that after you complete the first missable quest (Fireworks In A Bottle), you should start Fireworks For A Steal, and the following walkthrough explains how to complete it.
Description: “Just off Hawker’s Row in the Glutton’s Quarter, Lightning meets Funicula, a fireworks lover set to open the world’s first fireworks specialty shop…except that his entire stock has been stolen by monsters. Can Lightning recover the fireworks before the time runs out?”
Requirements: Start at 7 PM, end it before 3 AM, during Main Quest 2-2: The Legend Of The Savior.
Rewards: 1300 Gil, Maximum HP + 80, Strength +8, Magic + 4, Vanguard Headdress
According to the quest’s description, you client is named Funicula who spawns between 7 PM and 3 AM in Glutton’s Quarter, the area south of Yusnaan Train Station.
If you completed the Family Food side-quest, you should already know Glutton’s Quarter, but if you didn’t, then you will have to open your map, and notice the 5 restaurants on the left side of the main street.
Three of them are grouped together next to the General Store, while two are located in the south-western corner of Glutton’s Quarter. Between the two groups, to the west is a tunnel that allows you to reach the Slaughterhouse, in western Yusnaan.
The tunnel is also known as Road To War. When you are close to its entrance (in Glutton’s Quarter), on top of the stairs, with his back against the wall stands Funicula.
He wears a yellow shirt and has a crown made of fireworks. Let Lightning talk to her client and you will find out that he needs his fireworks back, which have been stolen by a beast. To retrieve Funicula’s Fireworks, follow the Road To War and soon you will see a Skata’ne.
Attack the beast and use fire-based attacks to stagger it, then defeat it and retrieve 5 fireworks.
Note: At this point you can keep the 5 fireworks and give them to the Fireworks Boss (Fireworks For A Steal failed), or you can give them to Funicula, and get 7 fireworks instead.
Return to your client, give Funicula the stolen goods, then follow him to his store and talk to him again to complete the quest and receive more fireworks.