Magic ink (汚れた墨, けがれたすみ, "Kegareta sumi") was formed when Kōtatsu placed a shard of the Shikon jewel in his ink jar. Although it looked normal at first sight, the ink needed a constant supply of human lives to sustain its life and would attack anyone if it was hungry. Moreover, anything painted with the ink came to life. Also, because of its mixture of blood and ink, it created a scent strong enough to knock Inuyasha unconscious.
- Among the yōkai that Kōtatsu creates with his magic ink include the guardians of Hell Gozu and Mezu.
- Strangely, Shippō, who has a strong sense of smell, is not affected by the scent of the Magic Ink. This may have been because he is not covered in it, or that his sense is not fully developed at the time.