Dieter first appears as a badly bruised kid stuck with a man named Hartmann, who's essentially trying to turn him into another Johan—a "perfect leader" type that the 511 Kinderheim orphanage never quite managed to produce before. Tenma rescues him from the abuse and Dieter becomes noticeably more hopeful afterward. He ends up tagging along with Tenma as he hunts for Johan, partly because he genuinely cares about the doctor but also because he's trying to keep Tenma from crossing a line and becoming a killer himself. Later, he becomes close with Nina, offering her support when her traumatic memories hit hard—which makes sense, since he's been through similar psychological torture and understands what she's dealing with.
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