Yuu Amanai is an apprentice and endorsement of Yuujirou Hanma during the Maximum Tournament. During the Maximum Tournament Saga, he was Yuujirou's comrade. Yuujirou met him in America, where he was serving as a bodyguard to the US president. The Ogre took him under his wing after Amanai kidnapped the president's attacker.

Amanai is a very unusual and ambiguous person. Outside the ring he is very friendly and seems to hate unnecessary violence, but in the ring he becomes unpredictable and ruthless. During the first round of the Maximum Tournament, he was kicking Minoru Yamamoto's face and knocked him out without a hint of concern about Minoru's life. Amanai stopped only because of an interference of the judges.