Mikado is Nigel Nesbitt's cat. She is first seen in episode "Shadow of a Doubt", when jumped on the desk and interrupted conversation between Nigel and Louis. Nigel started to apologize as a matter of fact that keeping animals in office is against the regulations, but Louis responded kindly and petted her, because he loves cats.
When Nigel left for a business trip to Pearson Darby's Hong Kong office, he asked Louis to cat-sit for a few weeks. Louis told Donna he was up all night with Nigel's high-maintenance cat – and he loved it. Later, in episode "She's Mine" Louis admitted to Rachel that Mikado was the only one to keep him cheered up during late difficult days. After Nigel returned from the trip, Louis hesitated to give Mikado back also because of the loss of his cat Bruno. He sued Nigel for neglecting care and they agreed to arrange mock trial – to decide who will take care of Mikado. Louis won, thanks to Rachel as his attorney, however, he agreed to give up Mikado to Nigel in exchange for getting back management of the associates.
In episode "Stay" Nigel said, that none of the letters Louis sent to Mikado was opened and also teared portrait he sent her, which irritated Louis.