Tsutsujidai was created by Akane Shinjo with the help of Alexis・Kerib in the Computer World as a means of escapism from her real life problems.
Anosillus the 2nd, who has been watching the unfolding of events for some time, seemed to be the only one to know of the reality of the city and everyone else lives their lives as if as if everything was normal.
Tsutsujidai is frequently attacked by monsters sent by Akane herself, for the purpose of deleting whoever and whatever she disliked, and the destruction would be undone by the 13 Venoras later on, with the monster attack victims having their history rewritten to have died years before.
Those same monsters also release gasses that make people fall asleep on the train, to prevent them from learning the truth of the city, as there is actually nothing outside. The train goes in loops until greater forces demand otherwise, and the outside world is destroyed by some means when the area no longer serves its purpose. Also, memories of the appearances of the kaiju and Gridman are erased by the next day.
After all the Venoras die out, the fog dissipates and reveals that the city is covered by a ceiling and outside of it is really the Computer World.
It is later revealed that the people are actually programs called Repli-Compoids (レプリコンポイド Repurikonpoido), that were made to unconditionally like Akane, while believing that they were real humans.
Tsutsujidai and the rest of the Computer World were repaired by Gridman via his Grid Fixer Beam in the finale, turning it into a replica of the real world. After Alexis' defeat and Akane's departure, the people of Tsutsujidai can live normal lives.
- In the original draft of Gridman the Hyper Agent F, the inspiration of SSSS.GRIDMAN, Tsutsujidai was the name of the industrial high school that Ippei Baba and Yuta Hibiki attend.
- Many of the places in Tsutsujidai are modeled after real-life locations.
- One of the stops for the buses and trains is Sakuragaoka, which is the city that forms the setting of Gridman the Hyper Agent.