Saiki Kusuo
Aren after transferring was alone and tried to make friends with Kusuo whom he sees as a loner however, the latter doesn't want to make friends with him so he instead rebuked Aren, making him angry and showing his true face. Aren admires Kusuo who has many friends when he saw him being crowded by Kaidou, Nendou, Teruhashi, Chiyo and Toritsuka. However, in later chapters Kusuo didn't mind anymore after he saved Kusuo and Kaidou from delinquents.
Kaidou Shun
Kaidou was the second person to know about Aren's secret of being a former delinquent.[1] Once when he saw Aren with a group of delinquents, Kaidou then concluded that he is a delinquent too and so he never wanted to befriend him. He was then scared of Aren but later on went friendly with each other after Aren saved him and Kusuo[2] from delinquents who tried to steal their money.
Nendou Riki
Aren thinks of Nendou as a strong rival or a delinquent basing on the latter's face. But later realized that he is a moron. Though he still sees him as a friend and tried to help him make money when he was trying to buy a gift for his mom.
Aiura Mikoto
Aren was shown to be not good with girls as when he was hugged and flirted by Aiura, he was having hard time and is stuttering.