Mr. Kay

Mr. K, known as Ukyo Kitano in the Japanese version, is a character appearing in Yu-Gi-Oh! ZEXAL. He is a professor at the junior high school Yuma Tsukumo attends, and was one of the characters possessed by the "Numbers". He seems to be the main teacher for Yuma's class, as seen during parent's day at Yuma's school.

In episode 23, Caswell asked him to help Yuma find The Emperor's Key using the Crashbug virus he created while he has a "Number", he was confused about this, but then accepted when Caswell blackmailed him with telling everyone that he is responsible for Crashbug virus incident. Using the virus, he located the Key and opened the door to the building where it was held for Yuma to go retrieve it.

Deck
Mr. Kay uses a Crashbug Deck revolving around Summoning his "Number" Xyz Monster, "Number 34: Terror-Byte". Much like the effects of his cards, his Deck represents what he has done - hacking into computer systems and taking control of them, launching "bugs" en masse, and wroughting many people (and the infected systems themselves) trouble because of it all.

Trivia

 * This character is often miswritten as "Mr.K" because of the similarity in sound.