"Kasa no Shita ni Ame ga Furu" is an original song by Ie no Ura de Manbou ga ShinderuP. As a character song for one of the protagonists in the story of his album Kowareta Sekai de Hana o Daku (壊れた世界で花を抱く), the song is featured on a CD as a gift along with the said album if purchased at Animate.
The song centers on the experience of Mikoshi Hinata (雛田ミコシ), God's secretary, on a rainy day as he is sent in place of God to descend to earth. At the beginning of the song, Mikoshi states he has innumerable reasons for his dislike against umbrellas, which is why he packs up his coat and holds it under his arm, searching for coverings from the rain as he walks in the street. As he does so, he sees a little girl alone by herself with her pink umbrella in her hand, who gets tripped by a rock hidden in a puddle. Curses the rain for being a sloppy system as an unceremonious creation by God, Mikoshi then sees the little girl's knee wounded and, to his dismay, even covered with mud. Then the little girl turns to Mikoshi, pointing her umbrella towards him as she tells him she has gotten lost from her mother, her seeking for help an action that reminds him of God, who always takes his help for granted. As he walks along with the little girl inside her umbrella, he discovers there to be flowers drawn by colored pencils on the inside of the umbrella. Boastfully, the girl tells him that these flowers are ones that only bloom on rainy days, which Mikoshi deems unfortunate as they can't be viewed from the outside. The little girl, however, with a smile, replies that that's fine, for her mother who has planted these flowers, for the purpose of letting them grow, made their roots face the rain. Eventually, they find the little girl's mother. And as the girl runs––carrying her wounded knee––towards her mother, who Mikoshi describes as has made the rainy sky the earth, the girl cries exclaiming that she's glad for it to be able to rain. Watching the admirable girl walk away with her mother, Mikoshi decides to put up his umbrella.