This article describes the story of Shuusou Gyoku in detail.
The game takes place on Earth in the future. The environment had nearly been destroyed, and humanity was on the verge of destruction. However, the Cactus Company perfected an energy source more powerful than the atomic energy. They used this power, known as cactus energy, to stop the ruin of Earth. However, this energy was very unstable, and caused large accidents. Eventually, it was controlled, and humanity began to prosper once again. Decades later, VIVIT, a robot "maid-type" powered by this energy, heads out to do errands for her master.
As she leaves to set out her errand, in which the errand is actually unknown, various people fight her for what appears to be no reason. Milia randomly stops her, claiming vengeance for her men, which VIVIT has no clue about. After that, she fights Mei and Mai. After that, she found a huge energy signature, which happens to be Gates, a military veteran. He dares VIVIT to show him her true power, and she does so, defeating him. Then Marie fights her in a gigantic ship in outer space, and dares her to go on, for the true terror lies ahead.
However, she's stopped as she goes deeper by her own master. He explains that this errand is to save his daughter, and that her previous enemies were tests. His daughter was sealed in an accident, and VIVIT's the only one who can save her. In one final test, she defeats her master, and goes to save his daughter in the Other Dimension, Vivit. As VIVIT finds Erich's daughter, she's surprised to see that Vivit looks exactly like her. She is suffering, and after a difficult battle, VIVIT manages to save her, completing her master's dreams.
VIVIT's errand has been completed and it was revealed that Milia, Gates, Marie, Mei and Mai were assassins hired by her master to test her abilities to see if she can save Vivit. It was said that Gates seemed to like VIVIT's powers, Mei and Mai went shopping with her and Marie has asked her out on a date four times.
VIVIT had commercial copies, and because of the likeness of her and Vivit, Erich didn't sell her copies as merchandises. VIVIT's also surprised on how similar and how much of a nice person Vivit is. After that, VIVIT was given another errand.
Continued after the Ending, VIVIT was given another errand to look for the Holy Grail for her master, but she left before he could explain that it was a joke. She decided to go to "the East" and went down the Silk Road where she eventually got lost. She eventually ended up at the Hakurei Shrine where there appears to be a pond and that she comes across Marisa Kirisame.
While chatting, Marisa insults VIVIT stating her as been a "cat-shaped robot". The two then battle and Marisa was defeated, where Reimu Hakurei jumps in, telling Marisa off for playing around the shrine. VIVIT tells Reimu that she really needs to fing this thing, but Reimu asks her to "come at me" and that she's got two sealing rods, stating she's extra powerful. After another long battle, VIVIT specifically tells Reimu that she's looking for the Holy Grail and that she needs to find it today. Reimu had no idea what it was.