After an accident in which a piece of shrapnel gets embedded in his brain, Hans loses all memories of his past. He was transferred from the regular police force in Germany and joins the A.D. Police as the resident rookie. His great sense of humor and friendly attitude make him much easier to get along with than Kenji. When he was transferred to Tokyo, he met Yuki Satomi, a Genom official who was posing as a nurse and instantly fell in love with her.
In episode nine, Hans is fatally injured by a rogue boomer. He survives somehow, but Kenji is wary about his rapid recovery and the fact that Genom took extreme measures to remove anything with Hans's blood. Using the blood Hans had on the jacket he was wearing during the attack, he has a test done. Hans Kleif is, like Liam Fletcher, not human, but a biologically fused boomer. Unlike Liam , Hans is not aware of what he is until Episode 11.
At the end of episode 12, Hans loses control and becomes a rabid boomer just as Liam Fletcher did. This implies that although he was the improved version of Liam, the the finalized version of the boomer is actually the body used by Kaibara. Losing control of himself and unwilling to let Kaibara escape, he forced Kenji to kill him and Kaibara.