Looks like in the anime lyrics/composition/arrangement of the song was credited to Centimillimental. However, on stores they are credited to Atsushi instead, i.e.
https://www.yodobashi.com/product/100000009003157970/
https://tower.jp/item/4925178/キヅアト＜通常盤＞
Not sure which way the booklet will have it written, but I have gone with the stores for now. As far as the actual accuracy of the credit goes it's all a bit irrelevant as Atsushi and Centimillimental are the same person.