Mr. Ikeda used to be one of Quasar's childhood school teachers. According to Quasar, instead of defending him from bullying classmates, at one point he joined in a game where everyone was pretending that Quasar had died.
Satoru and Koji also had sports classes taught by Mr. Ikeda. Koji once accidentally flung a baseball bat into his face.
In Number 9 Dream Mr. Ikeda is Miyake's sport's teacher and soccer coach.