Yuu Mashiro (真白 優) is a character in number24. He is a first year and plays in the scrum half bucks position in the Doshisha University Team. Due to his illness, he decided to become a manager like Natsusa Yuzuki.
Yuu is a young boy with smaller body. He has medium-long blue hair and green eyes.
Yuu admires Natsusa and wanted to play together with him, but as both could not play and he was reminded he loved rugby by Natsusa, Yuu decided to become a manager like him.
He has a vexatious personality ad he 'stalks' player's positions and analyzes them.
When Natsusa came back, Yuu was watching his video and got happy. During a training, he passed out and woke up next to Natsusa, who told him that he had passed out and it was likely due to anemia. Yuu explained he was behind the other team members and needed to train harder. Natsusa then teached him his phrases on how to get liked by his seniors. After that, they went to the hospital where Yuu was told he had anemia and gastric ulcer caused by malnutrition and stress. Yuu was frustrated, saying that he wanted to play with Natsusa and the others. Natsusa asked him if he loved rugby, as even though he can't play it right now, Natsusa still loves it. Although he realizes he was looking pathetic, he decided to not worry about it, as that would mean he loved himself more than rugby. He told Yuu that it will be hard for him to become regular, as there were many strong members in their school, but putting that aside, he asked him again if he loved rugby and Yuu told him he loved it. Yuu stomach then growled and Natsusa asked him if he wanted to go eat. Yuu wondered, since it was late, but Natsusa gave him a look and Yuu realized he needed to use the phrases Natsusa teached him before that and he accepted.
On the next day, Yuu announced in front of the team, he will be becoming one of the team managers.