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"Tenma told me, if you don't have any good memories, you can make some."
- Dieter, to Nina Fortner and Jaromir Lipsky

Dieter is one of the main supporting characters and an ally of Tenma, Nina and many others. Dieter was originally found by Tenma, where he was living with and being abused by Hartmann. Tenma saved him, and Dieter accompanied him for much of his journey. He would also help Nina when she was searching for her past.