S04E89: Piano of Sorrow

In this episode, Tsuna and Yamamoto learn about Gokudera's past. It is revealed that Hayato is an illegitimate child, born of Bianchi's father, the head of their mafia family, and a famous pianist. It is revealed that she died in a car crash when Hayato is still young. Hayato doesn't find out that she was his mother until years after the crash, but when he finds out, he runs away from home. After learning Hayato's history Glo encounters the past Chrome.