As the Spirit Detective of Earth, Yusuke Urameshi and his friends fight many fantastical battles against demons and even humans to protect the world from certain doom. Overseeing all the events of Yu Yu Hakusho is Koenma, ruler of the Spirit World and the godly being who helped Yusuke come back to life after his untimely death in the series premiere.
Though he has the appearance of a toddler -- as Yusuke and Kuwabara love to point out -- he is over 600 years old and manipulates his appearance into that of a young adult for more public matters. Though he is not a fighter like the others, Koenma possesses an incredible amount of spirit energy, transferred through the pacifier he always keeps inside his mouth. But why does Koenma use such a curious weapon? What exactly does it do?
The Koenma's Pacifier Holds Divine Energy
The pacifier, also known as the Mafuuken, is the source of Koenma's power and the single most powerful defensive weapon in the Spirit realm. Its greatest abilities are the restoration of life and the creation of a Kekkai (net-like) barrier even stronger than the one that keeps the human and demon worlds separate. The barrier creation in particular requires an immense amount of energy to work most effectively, and is intended for use only in humanity's gravest moment.
Koenma relies on the pacifier because his power is purely spiritual. He's not a physically gifted fighter like Yusuke, Kuwabara, Kurama or Hiei. Despite being a god in his own right, during the Dark Tournament's final round Koenma even doubts his ability to defeat the common human Sakyo in hand-to-hand combat. His abilities are predominantly defensive, as shown when he erects a formidable barrier to protect Team Urameshi from one of Younger Toguro's energy attacks.
Koenma Only Uses Mafuuken In Desperate Situations
Koenma has fed the Mafuuken with his own godlike spirit energy for hundreds of years in anticipation of the humanity's next Dark Age. It was predicted to come long after Yusuke and the main cast had come and gone from the world, but the Chapter Black Saga forced Koenma's hand sooner than expected. Due to his guilt over the actions and moral downfall of his previous Spirit Detective Shinobu Sensui, Koenma personally aids Yusuke against Sensui by removing the pacifier from his mouth.
He uses it to seal Sensui within a barrier strong enough to encase even the most powerful S-Class demons. However, Sensui harnesses his own unique brand of Sacred Energy and breaks free of the barrier, showing just how grave the situation had become. Koenma later uses the Mafuuken's restoration ability to revive the young human boy Amanuma, aka Gamemaster, who was killed by Kurama on the way to reaching Sensui.
For all his laziness at work, his occasional vanity and hilarious banter with the ogre Jorge, Koenma makes a number of brave decisions to aid and protect Yusuke on his Spirit Detective journey. When his own father King Enma demanded Yusuke be killed after revealing his Mazoku (demon) bloodline, Koenma openly defies his orders and supports Yusuke at the risk of his own life. In a way, the Mafuuken is a physical representation of Koenma himself: small (most of the time) but immensely powerful, and a symbol of protection and guardianship.
Now, explaining Koenma's ability to speak clearly with the Mafuuken in his mouth? That's a mystery for another day.
