The Ma Fū Kan (魔封環, translated as Demon Seal Ring[also known as Mafuuken/Mafukan in the FUNImation dub]) is the most powerful defensive spell in all creation, and Spirit Realm's last, best line of defense. It is a swell of pure Spirit energy, often focused in a relic. It also has other uses, including the ability to restore life to the deceased. In the case of the example seen in the storyline, it is contained in Koenma's pacifier, and had been storing his energy for centuries. Koenma was forced to use it against Shinobu Sensui, renegade Spirit Detective, but to no avail. Due to Koenma using a portion of the stored energy to resurrect Tsukihito Amanuma, it was greatly weakened, and the spell easily crushed by Sensui.