U.A. High School
Mei frequently invents a lot of inventions at U.A. High School, even during her break. As a result, she spends a lot of time in Power Loader's workshop and in his company. Power Loader tolerates Mei's presence and values her importance to the students.
However, when her behavior gets out of hand, he tries to keep her in line much to Mei's dismay. Despite that, the two are friendly with one another, with the occasional petty arguments that happen because of Mei.
Mei and Izuku first met during the U.A. Sports Festival. Mei took an interest in Izuku when he got first place in the Obstacle Race and as a result, got the ten million point headband. She saw this as an opportunity to bring attention to her inventions by using Izuku and approached him before the Human Cavalry Battle. In return for joining his team, she offered him and the other teammates support equipment to aid in their battle.
After the U.A. Tournament, the two would not meet again until Izuku wanted Power Loader's help in improving and redesigning his costume. Mei recognized him during their second encounter, but does not remember his name and dismissed it in order to go back to her inventions only to return her attention back to him when he brought up his purpose for entering the workshop. She provided Izuku some options for improvements on his costume and created Izuku's Costume Gamma.
Overall, the two generally get along well as Izuku has no problem talking with Mei during their first encounter. They got acquainted over a jet pack Mei created that was similar to a hero Izuku was familiar with. Izuku also appears to tolerate Mei more than some of his classmates like Tenya and Ochaco, since he shares some similarities to her as he creates ways to counter the quirks of others and rambles on as she does about gadgets.
Afterward, she has now gotten used to him and gave him some new gadgets for his training and used his last name, meaning she has gotten over her previous mistake. Izuku is still friendly to her though he is put off by her habit of getting in his personal space.
Ochaco has a somewhat rocky relationship with Mei, due to her direct nature. During her interactions with Mei, Izuku was always present as well and Mei often went awfully close to Izuku, much to Ochaco's dismay. She was slightly jealous when Izuku praised Mei's "super cute babies".
During their second encounter, Mei landed right on top of Izuku and shortly after, Mei felt Izuku's body and noted that it's surprisingly muscular. At the same time, she got a clear view of Mei's cleavage, shocking Ochaco after seeing the size of Mei's breasts. All of that made Ochaco visibly uncomfortable but she managed to remain polite and civil.
Mei approached Tenya before their match with Mei offering Tenya support equipment. Tenya naively accepted her supposed generous offer, only to realize too late that she was using him to promote her inventions. Despite her apology, Tenya dislikes Mei for taking advantage of his noble nature.
This dislike still remained with Tenya as seen in their second encounter. His dislike for her escalated when she forgot and dismissed his name, and also made him unwillingly use one of her inventions that he rejected. He openly voiced his dislike of her to Power Loader.