What Are Soul Seeds?In any chaos zone there will be 1-3 Soul Seeds on the ground. A quest in Luxerion you probably did on Day 1 gave you an introduction to them.
In a play through the game, I had about 40 at the start of Day 8 with essentially all quests complete. So you'll need to farm 10+ for this achievement and 60+ to get an Elixir, which meets the requirements of another achievement.
What are the Rewards?Talk to Soul Seed traders to trade in Soul Seeds for gold, as well as special bonuses at specific milestones.
At 20 soul seeds, you get a Hero's Potion (Refresher in NG+)
At 40 soul seeds, you get a Crusader's Potion (Ether in NG+)
At 60 soul seeds, you get an Ether (Phoenix Wing in NG+)
At 80 soul seeds, you get a Phoenix Wing (Elixir in NG+)
At 100 soul seeds, you get an Elixir (Turbo Ether in NG+)
The actual difficulty you play on does not matter. However, the NG+ values only apply if you got the first item in your first playthrough. For instance, if you only got 40 soul seeds your first playthrough, you will get Refresher and Ether for 20 and 40, but another Ether at 60. Effectively, all this means for you is that there's no way to avoid farming 100 soul seeds.
These two achievements are tied to Soul Seeds:
How to Farm Soul Seeds1. Complete Main Quest 2-1.
2. Complete "Death Safari". You can pick up the quest from the guard in the industrial area in Yusnaan.
3. Start "Death Game", located near the entrance to the industrial area, just South of the previous quest giver.
4. Search this area for Soul Seeds. There should be 2-3 of them. At this point, other guides will have you wait an hour of in-game time. We'll do something different.
5. Wait 1 hour of in-game time, then enter combat. When you leave (either by using escape or killing the enemy), the Soul Seeds will have respawned.
6. Keep collecting, waiting and escaping until Death Game automatically fails. Restart the quest and continue until you have enough Soul Seeds.