Heeeeeeeeere's... Dust Sans! He kills everyone in the Underground to acquire LV. He did so to hopefully put a stop to the human's genocidal actions, and he will do so no matter the cost. I totally didn't just copy and paste from the wiki... (just btw the bone in his hand is not very canon.)
You gotta wait about 7 seconds for the music to start (loud warning!). music by ReveX.