Arima's father is fucking CRAZY GAR. He does reconcile with his dad (and gave Yukino a gun for the LULZ).
But Arima's father was being blackmailed by his mother for money as 'child support' that she used on himself. Arima's dad decided to visit his mother saying that he won't get blackmailed again and finds a starved, bruised and nearly dead Arima in the apartment. He called his older brother (who is Arima's adopted father) and asked him to take Arima. His older brother agreed on the contingency that Arima's real father is not to make ANY contact with Arima because Arima's father was too young to care for a kid (IIRC, Arima's father was 14-15 when Arima was born). So to hold up his end of the deal, Arima's real dad moved to the states to become a famous pianst.
When Arima was starting to get media coverage, Arima's real dad decided to return to Japan and kill Arima's mom in case she started to exhort from her son. And he was seriously going to bust a cap in that bitch's ass until Arima told him to let her go. Arima's father said if the bitch ever approach him again, he will kill her.
Arima's bitch ass mother never came close to Arima again.