Atsumu is a childhood friend of Jinta and Menma. In the present, Atsumu holds a condescending attitude towards Jinta. He becomes agitated when Menma is mentioned and is still distraught over her death. He, together with Chiriko, attend the same high school, which Jinta failed the entrance exams to enter. Atsumu and Chiriko were once mistaken as a pair.
Atsumu is still in love with Meiko despite her death and keeps one of her sundresses in his closet. He buys hair scrunchies and other trinkets to place at her grave. He revealed that he is able to see Menma too.
But in the end of episode 4, it's been proven that he is a crossdresser and tried to fool everyone. Once they got him, Atsumu confessed his love for Meiko and that he felt guilty for her death.
In episode 5, Atsumu seems to have a kind of interest for Naruko, asking her to go out with him and if she is a virgin.