Believe in your own child

Yankumi is struggling through parent-teacher conferences, but when it's time for Sawada's meeting, his parents don't show up. Later, he receives a visit from a girl who turns out to be his sister. Through these incidents, we learn that Sawada lives alone due to a falling-out with his parents. When his sister takes an unnecessary risk, Sawada steps in to save her, but ends up shouldering the blame and getting arrested. The next day, the head teacher announces his expulsion. Can Yankumi and the boys of class 3-D do anything to help?