Jonas, son of Hannah and Michael Kahnwald, is a quiet, thoughtful teenager. The suicide of his father hits him hard and he struggles to process it, even after several months of therapy. In the days following Mikkel Nielsen's disappearance, Jonas' true purpose is revealed: He is a time traveler. He isn't yet aware of how significant a role he will play in the overall course of events.
Jonas was the last person to see Mikkel Nielsen before he vanished in 2019. When visiting the caves as a group, they were frightened by an unusual noise and started running through the forest. Magnus, Bartosz, Franziska, and Martha were ahead of them. Jonas tripped and suddenly Mikkel was gone.
The journey begins
A few days later, Jonas receives an anonymous package from the Stranger. It contains a futuristic light, Geiger counter, and goodbye letter from his father. The letter reveals that time travel exists and explains what's happened to Mikkel. Jonas finds the passage in the Winden caves thanks to a map his discovers in his father's room. He enters it and travels back to 1986.
Jonas finds Mikkel in the hospital there, but before he can do anything, the Stranger appears and warns him that Mikkel must become Michael Kahnwald in order to be Jonas' father. Jonas thus abandons his plan to rescue Mikkel.
Martha Nielsen is the love of his life. In the summer of 2019, it looks as though Martha and Jonas are going to become a couple, but his father's suicide shakes him. He spends months in therapy and stops answering her texts. Martha believes Jonas is in France and starts dating his best friend Bartosz Tiedemann instead.
When Jonas returns, their love is rekindled. That's until Jonas finds out that Mikkel is his father, making Martha his biological aunt. Without giving her a reason, Jonas blows her off and vanishes from Winden completely – but he never stops thinking about Martha.
His older self
On another trip to 1986, Jonas is intercepted by Noah and Helge Doppler. They knock him out and lock him in the bunker with the deadly time travel chair. The Stranger appears and reveals that he is indeed a grown-up Jonas, but he doesn't help the teen escape.
When the Stranger later tries to close the passage, a portal opens in front of Jonas' eyes. He can look into 1953. There, he sees Helge Doppler in the bunker as a boy. When their hands touch, Jonas lands in 2052.