I loved it soo much!!!
"Hugos" are weapons made by humans to use in wars and combating terrorism. They have a different sense of value and morals than humans (of course, they need to murder and may lose many colleagues during their missions). The retirement time for Hugos is after 120 years (at least).
The story is about Jan, a human, that bonded with two Hugos (a lion and a black panther). It's very sweet and dramatic - at the same time, and made me feel anxious as the protagonist was.
Really on my fav list, together with "Kuroneko Kareshi".
Hugo