The Flower We Saw That Day: Meiko Honma

Menma is a girl who suddenly appears several years after her death to Jinta and asks him to reunite their group of friends so her wish can be granted. Yet, she does not seem to remember what is her wish, but she knows she has to reunite her friends in order to remember. Despite being "dead", she is a very positive, energetic and lively person. According to Jinta, she is quite selfless and cries very often for others when they are hurt or upset, but not for herself. 
Jinta calls her "the beast of the summer" as he relates her to being a manifestation of his stress instead of a ghost girl. 

Poster