The cultivators Little Devourer had captured before, when they came to the Mist Hidden Sect's territory, had mentioned that there was likely a Saint-grade Heavenly Treasure in Myriad Skull Cave. However, neither they nor the sects and factions behind them knew what that Saint-grade Heavenly Treasure was. Now that the people from the Mist Hidden Sect had confirmed it was a Nine Nether Underworld King Flower, Ling Tian realized how important these people were. They and the forces behind them could be very useful in gathering intelligence. He was glad he hadn't killed them and had instead chosen to make use of their strength.
From the White Tiger Sacred Medicine's earlier reaction, Ling Tian could easily tell that even the Nine Nether Underworld King Flower would be hard-pressed to heal Lian Xin. But as long as it might help her, even a little, he would go find it for her. What's more, both the White Tiger Sacred Medicine and Wu Teng were certain that the Nine Nether Underworld King Flower could be very effective at treating even the most severe soul injuries. This only strengthened Ling Tian's resolve to seek it out.
Of course, even if the Nine Nether Underworld King Flower weren't a Saint-grade Heavenly Treasure, Ling Tian would still go looking for it. Finding it would not only further transform his Small World into a universe and increase his strength; most importantly, only by finding it would he have a chance to locate all 108 Saint-grade Heavenly Treasures and complete the "task" assigned by the Lord of the Universe. Only then would he have a chance to rescue Hua Min'er and his other friends and family from the universe.
As for the place where the Nine Nether Underworld King Flower grew, the extremely pure and dense Corpse Qi