Hello! My name is HMSquared, and this is my theory on the true story of INSIDE, and how it is connected to LIMBO since they were both created by the same company. (This is more like a story than a theory, so enjoy!)

My theory is that most of the world was destroyed before INSIDE began, and the government is creating the blob so they can take control of everyone left. The nameless protagonist is trying to stop the government because he thinks they killed his sister. When the boy finally gets mixed into the blob at the end of the game, he learns his sister is alive and that she was the long-haired character (or siren, as I call her) who was sent to kill her brother, but she helped him instead, which is why she is in the blob. When the blob finally rolls down the hill at the very end, the main character wakes up separated from the blob back in the cornfield. The main character does the secret ending, which causes the entire government complex to explode, killing all of the government people, but protecting everyone who was in the blob, including the main character, but changing their appearance so they are all pitch black. (This is my LIMBO reference.) There is a weapon that the other boys in the group (the sister is the only girl left) want to use but the sister wants to destroy. In the chaos, the protagonist gets shot and knocked out. The sister moves the protagonist into the woods, then hides in the wreckage, surrounding herself with glass and ordering the other boys to bring her her brother when he wakes up. The protagonist wakes up and begins searching for his sister. (LIMBO has begun.) The spider was somehow created by the other boys because they hate the protagonist, so they disobey orders. Eventually, the protagonist reunites with his sister, then both of them die after they learn that they were infected with a virus from their time in the blob. (A safety mechanism.) The brother and sister go to heaven, but the boy keeps dreaming about his time in LIMBO, which is why the game repeats.

I hope you liked this story, comment down below on what you think!