The Seed of Sorrow (悲しみの実 Kanashimi no mi?) is a cursed seed that takes root inside someone that eats it to sorrow and makes that sorrow eternal, even after death. The curse of surrow only disappears if the seed is extracted from the interior of the afflicted person.
Arae Aryrha2

Pulling out the seed

Princess Vajarois ate the seed in the last moments of her life after losing her friends so that through her sadness she did not forget them. The results were that the princess was turned into a ghost of grief known as Vajarois the Wailing. Her spirit was released after Akko, Lotte and Sucy removed the seed from her body.