Male Friends:
Yusuke Urameshi
He is 14 years old, a high school student and at the same time a Reikai Tantei. He's pretty popular in his school as a bully but he's a nice person. He was the one who helped save Kurama's mom by sharing half of his life to Kurama so the mirror would cure Kurama's mom. He's main power is the Reigun.
Hiei
I should say he's Kurama's closest friend. He's one of those who stole the Three Treasures in Reikai. Kurama stole the mirror and he was the one who took the sword. Later, became a Reikai Tantei. He has a jagan (third eye) which is very powerful. He's main weapon is his katana and has the ability to move fast.
Kazuma Kuwabara
A schoolmate of Yusuke and a Reikai Tan. He may look tough but he's really nice and sweet. He would do anything and fight for you if you are his friend. He's the weakest among the four but he has the biggest heart and that's what I admire in him. He's power is the Reiken (spiritual sword).
Koenma
The Reikai Tantei's boss. He is usually seen with a pacifier (Mafukan) on his mouth which is his powerful secret weapon. He doesn't know how to fight though. He just accompanied Yusuke and his company to the Ankoku Bujuutsukai.
Female Friends
Keiko Yukimura
Childhood friend of Yusuke and later became his girlfriend. She loves Yusuke very much and cares for him a lot. She gives him encouragement and support during fights. A nice, sweet, smart and responsible young woman who later marries Yusuke.
Botan
She is usually seen wearing a pink kimono dress and riding on a canoe flying in the sky. She is a spirit and the deity of death. She is Koenma-sama's messenger to Yusuke. But usually she's Yusuke's guardian. Always pictured with a cat face.
Yukina
Kazuma Kuwabara's beloved Yukina. A pretty, graceful and kind-hearted ice demon from Koorime. She left her home in search of her long lost brother who is Hiei. Only she and Kuwabara did not know that her brother is Hiei. When she cries, her tears become pearls that's why she was kidnapped.
Genkai
She is Yusuke's master. A pretty girl who used to work with Toguro but later left him. She's a Rei ki master so most people are afraid of her. She's a brave, strict and well-disciplined person and it really suits her to be a master for she is a good role model to Yusuke and the others.
Shizuru Kuwabara
A tough young lady who's little brother is Kuwabara. This woman can really kick ass and she is as strong as a bull. She loves her little brother so much that she even when to the Ankoku Bujuutsukai to support him.