Blue Spider Lily

The Blue Spider Lily is a mythical flower, said to look like a Spider Lily with blue colors instead of red. It has been described as a final ingredient for a medicine for Muzan's treatment by his doctor.

History
The Blue Spider Lily was a important base ingredient for the medicine of the doctor who treated Muzan's deadly disease. It was supposedly able to make Muzan walk under the sun again, without burning to ash. However the doctor has been killed by Muzan out of frustation, before he could finish the medicine. It was then that Muzan deeply regretted killing the doctor, as he then realized that his life saving treatment worked and that he had no idea how to finish his treatment by creating the medicine nor to find the Blue Spider Lily.