Koizumi Ichiro was shouting rhythmically over there, not so much for the physical pleasure, but rather for the psychological joy of success. He wanted to express all the joy in his heart, so he chose this way to do so.
Although he was writhing his body, perhaps there was no erection, or if there was, it was too small to elicit any reaction from the woman beneath him, which is why the female subordinate, despite being taken, had no reaction at all.
Koizumi Ichiro repeated the thrusting motions over and over, he wanted to trample the woman beneath him just as he would trample the Chinese people. In his heart, the Chinese were nothing but playthings under his crotch.
It's unclear how much time had passed when he finally grew tired and then lay on the bed laughing loudly. Lying there, he babbled for a while, as if talking to himself or to the female translator beside him.
