GodOfDogs
Haaaa this happens because as in his previous life he did not see the darkness of society and was not very old then he has to do a character development, that's why he was given a family, they killed her so that she can develop and does not think that the world is rainbow, nor that she believes that she has the power because she only has the future knowledge, this also happened because the family would be a hindrance where their enemies threatened them and would be their weakness.
Why Kill then he already had a goal to protect them and there’s no way someone just kills a god that’s stupid anyone who does will be hunted by every other god unless you are changing one of the most important rules of danmachi which prevent the gods from just wiping out each other over the smallest disagreement