|Spoiler Warning: Plot details, ending details, or both are in the text which follows.|
Modest Experiment is the twelfth episode of the anime.
Erna Tietze tells Tenma that Kinderheim 511 was a laboratory to create the perfect soldier. But when communism fell, all the East German officials involved in the project fled. Except for one: the former Minister of Health.
Tenma goes to Hartmann's apartment but neither Hartmann nor Dieter are there. Tenma then finds a series of pictures of several kids taken at Kinderheim 511, including one of Johan with an old man.
Tenma comes back to the Kinderheim 511 building and finds Dieter sitting on a chair next to a bonfire. Hartmann then arrives and tells Tenma that all the instructors and children of Kinderheim 511 died, and that Johan watched it all. Hartmann reveals that it was Johan who caused the fire at Kinderheim 511.
Hartmann tells Tenma that he does not think that he will be able to kill Johan and gives him a piece of advice: to find the man in the picture with Johan: General Wolf. After that, Dieter leaves with Tenma.
- Hartmann: "The world is pitch black. Tomorrow is full of darkness."
- Dieter: "Tomorrow will be a great day".