Nekomaru

Nekomaru is a bakeneko, a monster cat, who traveled with Ryunosuke from Shanghai to Kyoto. Nekomaru whines and cowers whenever there is trouble, which becomes more understandable as the series goes on because Gennai frequently uses him as a guinea pig.
Nekomaru is 300 years old and seems to have a fair amount of power. His most useful ability is being able to transfer one of his nine lives to someone who has died, resurrecting them in perfect health. He seems particularly fond of Ryunosuke and seems to want the young man to be happy.

(Source: Wikipedia)