Mei and Kouichi met in a very strange time in their lives. While death threatens class 3-3 in a house divided, it brings these two closer together.
Kouichi met Mei in the hospital where he was being treated for a collapsed lung. She was delivering a doll to her "Poor Other Half". He didn't think much of her until he was in school and seemed concerned when the other classmates acted as if they didn't notice her. He was the first person on screen to see what was behind her eyepatch something he inquired about in episode 2, but never seen it until episode 3 where she reveals the doll's eye. Because of the events of episodes 3 - 5 the students decided to give Kouchi the same treatment they gave Mei. As a result Mei was the only source of information that he had in regards of the class 3-3 calamity. They became close friends and by episode 12 he was willing to risk his own health and life to save Mei from both the curse and the remaining classmates who formed an angry mob.
There were some hints of romance between the two. In episode 6 Kouichi had a day dream where because he and Mei were Non-Existent they decided to use it to their advantange by dancing together, in front of the whole class. Early on he was the only person aside from Fujioka to tell her that her eye is beautiful. In episode 8 while making a sand mound with her on the beach, their hands connected in a sort of loving way. When one of the students knocked out Miss Mikami in front of Kouichi in Episode 11, Mei stopped Kouichi from fighting him and fellow students simply by grabbing his hand, prompting him to escort her to safety. During the early episodes, many of their dialogue scenes often have POV shots of Kouichi staring at her legs. Implying he might have a physical interest in her as well as a romantic.