He was considered as a quiet person according to the rest of Sakura's classmates.
He used to be in the same orphanage as Aoba and Maeshun.
He was thought to be Code:Revenger, until his identity was in revealed in chapter 107. He was another Re:Code agent. He was also given the task to look after Ogami. He even said he wanted to handle Code:Revenger himself. Later he walks to the school gates heavily injured, where he states that Aoba has retreated to Heisei Gakuin High School and that he can still stop her. He was then seen being assisted in walking by Maeshun. He states that his house is next to Aoba's. In chapter 143, he helps the group escape from Kagerou's Satan's Blaze by using exchange to transport him and the others to Kibou High locker room. He is with the others when people start to stare and say they are cosplaying. He then accompanies them through the halls. Later it was seen, that he had his head down from exhaustion in a classroom.
Uesugi's special power, Exchange (置換, Chikan), which allows him and others to switch places with an object he has marked beforehand. He calls out a word to select which object he wants to switch with like "Alpha" or "Gamma".
Aoba is his chilhood friend. They grew up at the same orphanage and were both witness to when the church was burnt down. When they were around 3-4 years old Aoba made Uesugi into one of her nakama after having defeated them in a fight. She decided that Uesugi and Toshiya were different from other boys so they were allowed to be her servants. Uesugi was there when Aoba swore revenge and also seemed to be aware that she had become a Code:Name. He kept her secret however and only revealed it much later when Ogami was targeted by Eden. Uesugi said he wanted to protect Aoba even if he had to oppose the other Re-Codes.
Toshiya grew up at the same orphanage as Uesugi adn Aoba however it seems he wasn't there to witness the church burning down. Toshiya helped Uesugi fight Aoba when she beat up the other boys that had been mean to the other girls at the orphanage. Just like Uesugi, Maeda was made into one of Aoba's servants at the same time as he was. Since then Toshiya has shown to be slightly jealous of how much closer than he, Uesugi, seemingly is to Aoba.