Seeds of the World Tree (世界樹の種) is a World Item that existed in YGGDRASIL.
Like any other World Items out there from YGGDRASIL, it can be found and acquired by players in the game.
Suzuki Satoru considered the idea that maybe this World Item could somehow allow even the undead to freely change their race without problem. Hence, in order for a YGGDRASIL character who had become undead to turn back into a human again, they would need to utilize a World Item like it.
- This is considered as the first World Item to have been mentioned in the Overlord Bonus Volume.