Mikkel Nielsen was the son of Ulrich and Katharina Nielsen, and brother of Magnus and Martha Nielsen. On November 4, 2019, he went into the Winden Caves with his brother and sister. The group scattered after hearing loud roaring, and Mikkel disappeared.
Mikkel, awaking in the cave, ran home but did not recognize its residents; Ulrich dismisses him. He observes the date on the newspaper at the door— 5 November 1986— but does not understand its implications. He goes into town to find his parents; unable to find his mother at the high school, he goes to the police station to look for his father, where Egon Tiedemann believes Ulrich is forcing Mikkel to participate in a prank. Seeing files about the missing Mads Nielsen on Egon's desk, Mikkel realizes he is in 1986. Ines Kahnwald, the nurse, takes him to the hospital, where Mikkel tells her he is from the future, but she does not understand. He flees the hospital at night to return to the caves, but is unable to return, and breaks his leg. He is returned to the hospital, where Ines introduces him to Noah, and they have a discussion about the creation of the universe.
Ines eventually adopted Mikkel and raised him as Michael Kahnwald; he remained in the town, married Hannah, and fathered Jonas. Never at home in his altered timeline, he committed suicide on June 21, 2019.