I think Aramaki may be the son of Mjosgard.I think that Mjolsgard had a baby with one of his slaves.I think that in that type of predicament the child would be viewed as a type of demi god.But remember that the celestial dragons do not view people from below the red line as anything less than insects.
Also keep in mind that Mjosgard would have obviosly not given a damn about his wife/slave back then.Either way i don't think that he would wanna execute his son.So he probably let his wife/slave leave mary geoise or he shoot her in the head.Either way i don't think that he would resent his son for being born.
Because as i said his son would have been viewed as a demi god in the eyes of the celestial dragons.He's still not regarded as an equal in their eyes but they won't execute him because of his ties with Mjosgard.I also think that he wouldn't be capable of being the head/leader of his family.Strictly because of his half blood status.I also think that this may play into another theory of mine.I think that the celestial dragons born with a half blood status are forced into military servitude.As they are viewed as demi gods they're role would be to defend the country of mary geoise against other external threats.I think that's the reason for why Aramaki was getting so heated about that argument with yamato within the latest chapter.As he has learned the true history of the world from the celestial dragons while being raised within mary geoise.
I think that's why he views his military service as a type of obligation to his country.Because that's how he was raised.That said that leads me to my last theory.I don't think that the celestial dragons are forbbiden from executing one another.I think that within the case of a slave executing a celestial dragon even if it's upon the orders of another celestial dragon it would be regarded as treason.However i also think that if a celestial dragon executes another celestial dragon on their own it would be regarded as a god slaying another god.Metaphoricaly putting that god into a higher state of power within the eyes of other gods/celestial dragons.Also while i do think that Im-sama might be older then he's letting on.I still think that Im may have become the king of mary geoise strictly because he has been the person who has executed the highest number of celestial dragons.