Non-spoilers, but based on speculation after reading the first two chapters:
Obviously the emperor is behind the attack, because he wants Chester to be fully devoted/loyal to him and only him by killing off his real family and the girl her likes.
Since it's also obvious he killed his own father...
Kinda looks like a Shield Hero ripoff, but not terrible off the bat yet.
Will have to see how big his harem gets and how many female party members he gets lumped with and how generic and boring the rest of the events are before dropping this.