Once, there was a group of close childhood friends. However, by the time they entered high school, they had grown apart from each other. These are:

Jin-tan — The hikikomori.
Anaru — She just wants to hang out with her girlfriends.
Yukiatsu and Tsuruko — These two are proper school-going students.
Poppo — Rather than enter high school, he had opted to do some travelling.
Menma — The one unchanging constant of the group.

One day, Menma meets Jin-tan and asks him to fulfil her wish. For this, these widely separated companions gather once more.