Mr. Akashi (明石) and Mr. Iwamoto (岩本) are two teachers that Yusuke does not get along with. Mr. Akashi and Mr. Iwamoto hate him and his friends. They try every trick in the book to expel them. During the Four Beasts saga, Mr. Iwamoto is infested with a roundworm monster/makai insect. Since Suzaku commanded all of the infested people to kill Keiko Yukimura, Iwamoto stalks Keiko around Sarayashiki Junior High School before Yusuke destroys the whistle, which causes the insect inside him to die; he returns to normal afterwards. Yusuke first tested his spiritual powers by firing his Spirit Gun into the back of Iwamoto's head, knocking him out.

Urameshi Yusuke, 14 years of age, is about as troublesome and violent as teenagers come. He is constantly ditching school, causing trouble, and getting into numerous fights everyday. One day however, he does the unexpected, sacrificing himself to save a young child. Such an action, was never ever expected, especially coming from someone as troublesome as Urameshi Yusuke. The afterlife is not prepared for Yusuke, as they never thought he would make such a sacrifice. Nowhere to go, and dead, Yusuke becomes a ghost and must earn his way back into existence. 
Yusuke is "employed" by Koenma, who is in charge while his father and ruler of the afterlife, King Enma, is away. Under Koenma's command, Yusuke helps to stop menacing demons that threaten the lives of people everywhere; whether by stealing priceless and invaluable items and destructive weapons, or by wreaking havoc on humans everywhere. 
Throughout Yusuke's journey, he is usually joined by; his arch-rival, and local bully, Kuwabara Kazuma. He is also joined by two demons named Hiei and Kurama, whom are ex-convicts of the afterlife that managed to escape from Koenma. 
This group of unlikely allies goes on to participate and struggle in battles that have outcomes that determine the fate of humanity! 
(Source: AniDB)

Yusuke Urameshi was a tough teen delinquent until one selfless act changed his life...by ending it. When he died saving a little kid from a speeding car, the afterlife didn't know what to do with him, so it gave him a second chance at life. Now, Yusuke is a ghost with a mission, performing good deeds at the behest of Botan, the ferrywoman of the River Styx, and Koenma, the pacifier-sucking judge of the dead.
 
(Source: Viz Media)
 
Note: Chapter count includes one extra chapter.