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Banjo-Threeie is a fanon 2018 (set in 2002) game, made to erase Banjo-Kazooie: Nuts and Bolts from canon. It takes place two years after Banjo-Tooie, with the exception of a cutscene at the beginning in which Mumbo Jumbo and Humba Wumba combine their powers to restore Banjo's house (and make peace between each other), and the Grey Jinjos and their house being restored with the B.O.B. It is comprised primarily of assets, characters and level design inspired and/or taken from the first two games, which can be seen heavily in worlds two, three and nine.
Two years after Grunty's defeat at Cauldron Keep, Banjo, Kazooie and Bottles are in Spiral Mountain one day when Bottles challenges Banjo to find the Ice Key that he hid somewhere in the mountain. When Banjo finds it, he is told that he can indeed access the blocked off areas of Grunty's Lair, where he finds a portal to a re-developed Jinjo Country (known as Jinjo Kingdom) that has been taken over by Klungo's still evil son, Splungo. When (former) King Jingaling tells them of his misfortunes, they set out to save the Jinjos, with the help of the Jinjonator from the end of Banjo-Kazooie (which is powered by nothing less than the good ol' Jiggies), which smashes open world doors and, eventually, Splungo's throne room.
Directly following the events of Banjo-Tooie, Banjo, Kazooie and their friends come home from Cauldron Keep, not before restoring the Grey Jinjo family. Humba Wumba and Mumbo Jumbo are shown to put aside their rivalry and begin to work together for good, and they combine powers to restore Banjo's house to its original form. Tooty is seen to be living in Click Clock Wood next door to Nabnut.
Two years later, Banjo, Kazooie and Bottles are outside of Banjo's house in a now almost completely restored Spiral Mountain. Bottles challenges Banjo to find the Ice Key that Bottles hid somewhere in Spiral Mountain, chosen randomly between three places: the crevice behind the large waterfall, the hole at the bottom of Spiral Mountain or inside the hole in the Veggie Garden (accessed by Bill Drill). Bottles continues to tell them that a window on Grunty's statue entrance to her (now blocked off completely) old lair is, in fact, breakable. Using the Flight Pad on top of the Mountain, Banjo and Kazooie make their way to it and go inside, where they find the Transformation Room where Tooty's beauty was going to be swapped with Grunty's all those four years ago. Much to Banjo and Kazooie's shock, one of the doors in that room is unlockable with the Ice Key, and when they go in they find themselves in the first part of the game's Hub World, Jinjo Kingdom.