Yuu Amanai (天内 悠, Amanai Yū) is an apprentice and endorsement of Yuujiro Hanma during the Maximum Tournament. During the Maximum Tournament Saga, he was Yuujiro's comrade. Yuujiro 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.
But at some point of the second round of the tournament, Amanai started to worry about Doppo Orochi. He even said that there is no way for Doppo to beat him due to the injuries, and repeatedly begged Mitsunari Tokugawa to stop the fight and declare him the winner. It is possible that Amanai's concern was due to the fact that he had a different attitude to Doppo than to his previous opponent. Before the start of the fight it was seen that Amanai has great respect for him.
He follows his own philosophy, which says that the key to defeat an enemy is the ability to understand an opponent's feelings and desires. He claims that his theory is based on love.
Yuu Amanai is half-Japanese half-American, he is a tall and slim individual with long legs. His physical condition and leaping ability allows him to stay in air for a some period of time. One of his most prominent physical features is his blank and emotionless stare.
Amanai Yuu practices his own fighting style, which utilizes the user's jumping ability to allow him remain airborne for a some amount of time. While airborne, Amanai starts to kick his opponent. In the manga series, his fighting style was listed as the Amanai-ryuu Martial Arts (天内流格技, Amanai-ryū Kakugi). His style is based on love in contrast to Yuujiro's style which is more aggressive and based on rage.