Rensuke Kunigami is a wealthy and successful businessman in the novel "The Housekeeper and the Professor" by Yoko Ogawa. He is portrayed as a brilliant mathematician who has a passion for numbers and equations. Despite his intellectual prowess, Rensuke suffers from short-term memory loss which limits his ability to remember new information beyond 80 minutes. This condition poses a challenge for him in forming new memories and maintaining relationships. Despite his struggles, Rensuke is shown to be kind, gentle, and caring towards those around him, especially the housekeeper and the professor who play significant roles in his life.