Tom hadn't heard much of the situation, he was passing through the house, looking for food to give Max when he saw Kou, and Kozue, and the others. Before Tom had joined the group, he would have continued on, he was aloof, alone, and neutral. Had he gotten involved, he would have investigated to see who was the most deserving of blame.
But suddenly he felt himself filled with anger. He remember the time in Keiichi's dungeon, when Kou told Kozue she had looked better. that she some how needed to change, and he couldn't accept who she was, because who she was, was special. She was his friend, and Kou, who hadn't cared about her in Keiichi's dungeon, who couldn't accept who she was, now had the audacity to insult her.
Without realizing how he'd moved, Tom stood between Kou and Kozue, fists clenched, and a scowl on his face. Max was at Tom's heels tail down, looking between the two men.