Mugi first met Yui back in the Light Music Club room and had spoiled her with sweets and drink so that Yui would be interested to join the club. After joining, Mugi had done quite a lot of good action to Yui, such as lowering the cost of the guitar when Yui was about to buy her first guitar.
Yui always wanted to taste more of Mugi's cake and can't wait to eat it, it is said that without Mugi's snacks, she won't be able to play the guitar properly.
Mugi sometimes can get very annoyed wondering about Yui's fast metabolism.
Mio first met Mugi when Mugi originally intended to join the choir club. Mugi later joins the Light Music Club only after witnessing the "fun and painful interaction" between Mio and Ritsu. Mio and Mugi had been good friends, but sometime Mio founds Mugi to 'betray' her, such as, when taking vote of either to play in the beach or to practice and Mugi decided to play with both Ritsu and Yui and Mio thinks she betrayed her (in kind form).
Like Mio, Mugi is very concerned about her weight, and both are jealous about Yui's fast metabolism.
Ritsu first met Mugi when Mugi originally intended to join the choir club. Mugi later joins Light Music Club only after witnessing the "fun and painful interaction" between Ritsu and Mio. Ritsu had been polite to Mugi all along, until once when Mugi suggested that if Ritsu was a male and she would be really popular among girls. It was the one and only time Ritsu hit Mugi on the head and shouted at Mugi.
Mugi treasured her friendship with Ritsu very much as seen that she always enjoyed Ritsu's company. Being as observant and wise, Ritsu had brought Mugi to commoners' places like tuck shops and the arcade, as she knows that Mugi might not have visited those places before. Ritsu had once said that even without Mio, she still has Mugi to tutor her in her studies. Ritsu was shocked speechless when she first found out in a phone conversation with Azusa that Mugi's house had a housekeeper.
Azusa finds Mugi to be very beautiful, and envies her hair and large eyes, and later starts teaching her how to play guitar when the two are alone in the club room. She also finds Mugi's snacks to be delicious and enjoyed eating her snacks.
She is shocked to find out that Mugi's house had a housekeeper and is impressed with the villa that Mugi served to the girls during the training camp.