This was a Pseudonym used by Kotani Kinya for just the one Release shown below. MC-K2 was a Short for "Mother Complex" - Kotani Kinya. That makes him "Kotani Kinya, the Mother Complexed Boy", so to speak. He was also refered to as "MC-Rocker". In addition the official Fanclubs Name that Time was "MC-Pantei", which is the abbreviation of "Mother Complex Pank+Party".
MC-K2 was used as some kind of Trademark, since you can find this Short on all Releases by Antinos Records. ("WHAT? Physical" and "HISTORY P-20"). Kinya stopped using this Trademark, when he changed to the Label "R&C".
Legal name: コタニキンヤ