Professor Booster (ブースター博士 Dr. Būsutā) is a professor from the research team that went to the Island. When the Doctor gained control of the Demon Crown, he put Kazuma and Booster in jail. Kazuma managed to escape to a teleporter (most likely the one from Jail No. 2) warping him to Bushlands.
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After the player blows up the rusted door trapping Kazuma in a shelter, Professor Booster appears, seemingly having escaped. After a conversation with Kazuma, each of them go outside, and then Booster and Kazuma use a bike to quickly navigate out of the Bushlands. They lose control and crash in front of Santa's House.
You later meet them at Arthur's House talking about the Red Flowers and other things. He then sends you off to the Sand Zone to burn the Red Flowers. Later, while you're stuck navigating through the Labyrinth, Misery zaps him into the room right after Monster X. Now the player can choose two options. First, they can speak with Booster about his fall; he also tells you that you were teleported near the heart of the island, and he gives you his nearly complete invention, the Booster v0.8. Doing so causes Professor Booster to die. If you choose to ignore him (you can still beat the Labyrinth and the Core without the jetpack), he will stay alive and teleport back to Arthur's House. He then gives you the completely finished jetpack, the Booster v2.0, and also tells you to find Sue and get off of the island as fast as you can. He acts as Sue's grandfather figure.
|Cave Story Characters|
|Protagonists||Quote • Curly Brace • Sue Sakamoto • King • Toroko • Kazuma Sakamoto • Professor Booster • Itoh • Momorin Sakamoto|
|Antagonists||Doctor • Misery • Balrog • Ballos|
|Others||Tetsuzou Kamadani • Jack • Mahin • Kanpachi • Sandaime • Arthur • Cthulhu • Santa • Chako • Malco • Colons • Jenka • Puppies • Chaba • Dr. Gero • Nurse Hasumi • Littles • Chie • Zett • Megane • Shovel Brigade • Numahachi • Ballos|
|Races||Robots • Mimiga • Humans • Cthulhu • Witches • Gaudi • Droll|