Frostforged

Ryuunosuke found a stray cat, suddently gunfire broke out around them, he ends up getting away but the cat got hit by a bullet and ends up dying. A few weeks later, he gets a new sister, Nuku-Nuku, which turns out to be the cat inside of an android.

Junpei Kousaka is second-year high school student who is allergic to cats, making him hate anything and everything that has to do with them. Unfortunately for him, he is surrounded by cat-lovers; his family, his estranged childhood friend, and worse of all, her all time crush, Kaede Mizuno.

Ryuunosuke found a stray cat, suddently gunfire broke out around them, he ends up getting away but the cat got hit by a bullet and ends up dying. A few weeks later, he gets a new sister, Nuku-Nuku, which turns out to be the cat inside of an android.