Monster, Perfect Edition Volume 6 of 9 (by Naoki Urasawa)

The story follows Dr. Kenzo Tenma, a brilliant Japanese neurosurgeon working in Germany. His life changes forever when he follows his ethics and chooses to save a young boy's life instead of the town's mayor. Years later, Tenma discovers that the boy he saved, Johan Liebert, has grown into a charismatic, cold-blooded serial killer. Consumed by guilt, Dr. Tenma embarks on a dangerous journey across Europe to stop the "monster" he brought back to life.