[Note: This episode is a side-story that takes place between the first and second halves of the show. It was listed as episode #12.5 on Crunchyroll.]
This episode is told in reverse chronological order.
A man named Ginjiro tries to outrun a couple of bill collectors represented by Tom and Shizuo as his girlfriend tearfully explains what a fool she's been. As Anri, Kida and Mikado all plan to attend a summer festival, they get roped into cosplaying by an overexcited maid offering free drinks. Elsewhere, the van gang has a red bag on their van, because Walker and Erika believe that it will attract a UFO.
However, Celty also retrieves a red bag as part of a job with a hint that it might have a severed head in it. For some reason, this red bag makes her the target of two different groups trying to retrieve it: a Yakuza gang and a group of American smugglers.
It later turns out there are three different red bags in play: The bag that Ginjiro had with his clothes and some food from his girlfriend, the bag with a ton of cash that the Yakuza were collecting, and the bag containing a rare lizard inside. Izaya managed to play the different parties off each other with Celty's help, and he recovers the lizard from the smugglers. As for the cash, Shizuo's company receives it. When the Yakuza tries to take it back, Shizuo punches them so hard that they fly through the sky, appearing as UFOs or fireworks to any onlookers.
And Ginjiro? He gets back with his girlfriend, finding that she has the same bag as before after Anri and her friends found it near the festival. As the narrator says, "God is in his heaven, and all is right with the world."