Arthur

A stray cat which Third Princess Euphemia befriends after she arrives in Area 11. Arthur is later chased throughout the school grounds by the entire student body after wandering into the Lamperouge residence and escaping with Lelouchs Zero mask. The student council adopts him and builds a cat house in the council room. A running gag in the series involves Arthur constantly taking a bite at Suzakus hand or leg. Despite this typically onesided relationship Suzaku takes the feline along with him to Britannia where Arthur takes a liking to Knights of the Round member Anya Alstreim. When Suzaku returns to Ashford Academy in the second season he brings Arthur back with him. Source: Wikipedia