3 Idiots

Three bullies from Osamu and Yūma's school, who are collectively known as 3 Idiots. In the manga, their names are not given and are referred to as No.1, No.2, and No.3. In the anime, the credits gave them the surnames: Eida, Bitō, and Shīhara.

they all appeared in the first chapter and first episode

Trivia

 * No. 1 (Eida the redhead) is "Ringleader" of the group. He is the worst of all the delinquents but Ashihara wishes to improve his danger detection skills so he could survive.
 * His Japanese voice actor, Mitsuo Iwata, also voices Isami Tōma.
 * His English voice actor, Bill Newton, also voices Isami Tōma, and Kōtarō Suwa.
 * No. 2 (Bitō, brown hair) is "The Annoying One", The author doesn't exactly hate him however he finds him easy to draw.
 * His Japanese voice actor, Hiroaki Miura, also voices Ryō Utagawa.
 * No. 3 (Shīhara, dyed hair) is "Roots Showing". According to Volume 1, his delinquency is his hobby. He has good grades, and his family is quite rich.
 * His Japanese voice actor, Kōta Nemoto, also voices Ken Satori, while his English voice actor, Daegan Manns, also voices Reiji Kizaki.