Mount Hothead is a molten area that you can visit in Hello Kitty Island Adventure. When you first arrive, you may notice the lack of lava flowing down the mountain, but this isn't permanent.

Which, you've guessed it, you now need to go and build. Now that you've got your net, head back to Keroppi and Badtz-Maru in Lilypad Lagoon. Speak to them to learn that you need to catch a Lily ...

Once at the Comedy Club, speak to Hangyodon, then speak to Keroppi once he shows up. You will then need to head to the Sunken Ship in Rainbow Reef, speak to Keroppi again, and find a toolbox nearby.