Kazuya Tanaka is a minor character. During the Survival game, Tanaka asked Toki Nagayama out for a date. The manga hinted that it was caused by the Hanging Bridge Effect.
He became closer to Nagayama and is often seen together with her on the Trip to Kyoto, The Walking Festival, and in a empty room together (though we never see what happened there). They are sometimes seen studying together.