Dieter is a young boy age 11 with short red hair, light blue eyes, and pale skin.
Initially based on their mutual fondness for Tenma, the two develop a companionship not too unlike a sibling bond. Dieter even travels with her against her wishes. He cares for Nina's well-being as much as she cares for his, and by the end of the series, they maintain a close bond with constant communication when Nina is away at university.
Nina would eventually have some kind of relationship with him; she sees a future with him.
