Capricorn

Capricorn (カプリコン) is a five-volume manga series by Johji Manabe. It was later adapted into an anime OVA and released on April 5, 1991 by Aubec.

Plot
On an alternate world where the Earth named "Capricorn" can occasionally be glimpsed in the sky. The planet's inhabitants, ruled by a decadent king, are almost all intelligent, anthropomorphic animals; one exception is the human-looking Mona, a young and adventurous woman. Mona's scholarly friend, an elderly anthropomorphic mouse, becomes caught up in a conspiracy to replace the monarchy with a military dictatorship. Against this backdrop, two young Japanese suddenly materialise on the planet: the high-school student Taku Shimamura and his sister Tamaki.