Based on Chapter 1 of the MC's past before being reincarnated, I get the distinct feeling that he was the one who killed her father. As he did say he used to live for the thrill of the fight and to become stronger, even becoming a mercenary.
@Gladiator02 They're kid would be like Sakamoto but the exact opposite when it comes to luck. Constantly has a cool expression but is a huge klutz, but looks badass while doing it.