10 years before the events in Cave Story, Quote and his partner Curly Brace were sent to the floating Mimiga Island to destroy an artifact called the Demon Crown (rather than retrieve it, which all others were doing at the time). They found the man who had claimed it for his own and defeated him in battle, but were still somehow defeated afterwards. They were left in the caves filling the floating island to rot.
At the beginning of the game, Quote wakes up in the caves, not remembering anything. He leaves to find out where he is, and possibly who he is. He eventually finds he is in some island filled with rabbit like creatures called Mimigas. Recently, they have been terrorized by a villain known as the Doctor who kidnaps them in masses and sometimes even kills them. Quote begins to travel through the caves to find out who The Doctor is and how he can defeat him.
After finding Curly Brace (who also has amnesia) and some scientists sent to the island to study it, Quote learns more and more about what the Doctor is planning. He is taking the Mimigas and giving them a strange red flower to eat. After consumption, the Mimiga becomes enraged and very powerful. The Doctor wishes to use them as a living weapon, so he may rule the world. Quote also learns about the Core of the island, which abruptly attacked him and Curly once they found it. Unfortunately, if the Core is destroyed, the island falls. The Doctor comes and repairs it after it is nearly destroyed.
After these events, the player can chose one of 3 endings: good, bad and normal. In the bad ending, Quote becomes fearful and leaves the island, letting the doctor continue with his plans. In the normal ending, Quote defeats the Doctor, his assistant, and the Core once again. This, however, causes the island to fall, saving the world from the rabid Mimigas but killing nearly everyone on the island at the same time. In the good ending, the island begins to fall but Quote finds a secret passage leading back into the island. Curious as he is, he jumps in.
Here, he reunites with Curly (for, like, the 5th time) and learns the island's origins. It was apparently first used as a prison for an insane sorceror named Ballos. Ballos had lost control of his power, and was sealed inside the island by his sister as a result. Quote is determined to help Ballos, but there is only one way to ease him of his pain: to kill him and put an end to his magic. After he is found, Ballos reveals who he is and asks Quote to kill him, or he will kill Quote. After a long battle, Ballos is defeated and Quote, Curly and Balrog (a former forced antagonist) leave the island and find a nice place to live. The island also stops falling, due to Ballos' magic leaving him.
Quote is a silent protagonist, and he only has a couple of sprites in-game, so little is known of his reactions to many events. He is shown to be incredibly determined to do the greater good (unless the player chooses the bad ending) and seems to be very curious.
Due to Quote being created for combat, he is very adept with using all kinds of weaponary. He can use up to 10 weapons in-game and is also very strong. He is capeable of taking hits and dealing damage. He can also increase his health with health tanks and is strangely shown to have human emotions and biological functions, despite him being a robot.