Stratos and Delilah are a duo of explorers forming Team Slacker.
First, the team can meet them at Golden Settlement during its festival. Kabbu says they never finished their mission, but then it's revealed they just gather information of tough mission so that other explorer can finish it.
In Chapter 3, they are investigating Sand Castle, which is hidden except its top. At the end of chapter 3, by their scouting, it's revealed the half of the third artifact is hidden there and two special keys are required to get in.
After that, they appear near the Bounties and give Team Snakemouth some hints for finding them.