Mai

Mai, the middle sister, is a tomboy-ish 14-year-old girl. She has pink hair and usually wears sporty looking clothes. Mai is constantly reminded of her flat chest by her younger sister Mii which causes her to blow a fuse.

Early in the season she was acknowledged for having problems with constantly moving for which she got constantly depressed about to the point she refused to go to school. This was because she thought everyone hated her after making friends and then abandoning them. She understood the impact of their journeys on others, unlike Mii, but did not have the mental maturity, like Ai, to cope with it.

Later in the series she makes friends with a classmate of hers, Konami. When it was time to leave, Konami helped convince Mai that she was wrong and in consolation Mai left a sketch portrait Konami they were to make for a class assignment for Konami as a departing gift stating that they'll remain friends forever, even if they never see each other again.

(Source: Wikipedia)