Summer's Rain can be obtained by having Asagami Fujino reach Bond Level 10.
Summer's Rain is Asagami Fujino' Max Bond CE and exclusive to her.
Rashoumon event (Ibaraki Douji event)
Murder at the Kogetsukan
Inheritance of Glory
Darius III
Evil Servants
Ereshkigal
Arthur Pendragon(Prototype)
Gorgon
Black Holy Grail (The Black Grail)