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Bootmon was born from the Super Boot app created by Katsura Hajime. It has a childlike personality and voice.
Bootmon was born from the Super Boot App created by Katsura Hajime under orders from Leviathan. By being born that way, despite being an Ultimate, he had a child's innocence, voice, and personality. Before being taken by Leviathan, Hajime freed him and asked him to flee. As punishment, he was transformed into Sleepmon by Biomon.
Bootmon began to be sought by Appli Drivers, and was found in Appmon's Kindergarten, but was startled by Gatchmon, Musimon and Dokamon, fleeing the place. Bootmon was found again after Damedamon's defeat at a festival in "Pursue the Fugitive - Bootmon! ", but again fled after being frightened by the fireworks, and was not seen for a while.
In "The Truth About Yujin ", Gatchmon installs a hack created by Rei and Hajime that would bring Bootmon to where Haru was after its next escape. After being frightened by Eri and fleeing, Bootmon is drawn to the place where Haru and Yujin are, but is killed by Shutmon before Yujin reveals himself as a robot, servant of Leviathan.
In "Launch! The Humanity Applification Plan! ", Bootmon is infected by Yujin, becoming seemingly more violent, but still childish, and was used to activate the God Grade with the Deusmon's chip and merged with Shutmon to create Rebootmon's chip.
After Leviathan absorbed the God Appmon, like Offmon, it's likely that Bootmon has returned to normal as well, but he is only seen again in "Our Singularity ", making it clear that he stayed with Hajime forever, just like the other Buddy Appmon.