Mako is Tomoko's classmate and Yuri Tamura's bestfriend.
Mako is the the only character to have noticeable freckles.
Yuri and Mako eat lunch very often so it's likely that they are close friends, however that is not to say that they do not have their differences. They were having a fight before the school trip to Kyoto, which ultimately caused Yuri to be in Tomoko's group. They have since made up and continue their friendship, which has extended to include Tomoko in their daily lunches and even group texts (chapter 99).
Mako sometimes ends up having lunch with Tomoko through Yuri, but otherwise had never directly interacted with her. In chapter 99, when Yuri falls sick, Mako becomes overwhelmed with guilt for not having lunch with Tomoko after she mistakenly thought she saw Tomoko become dejected and start sobbing for being excluded: a repeat of what she did to Yuri during the school trip. She begs for forgiveness from Tomoko, who replies that didn't care anyway (in all honesty). Thinking Tomoko was lying to spare her feelings, Mako becomes convinced that Tomoko is a good person, and makes Tomoko her friend.
Minami and Mako are casual friends.