Gantz Wiki:Character Template (Human)
Tanaka is first seen in Joichiro Nishi's class paying no attention to him.
Plot
Italian Alien Mission Arc
He was most likely not present when his fellow Classmates threw Joichiro Nishi's desk and chair out of the window right when he was passing by, intending to hit him. However due to this Nishi took his seat instead leaving him without a place to sit.