The kanji isn't actually very similar--while English spells them similarly, "zawa" and "zaki" wouldn't read similar to someone who could read Japanese. Miyazaki is 宮﨑 , but Miyazawa is 宮沢. Pretty distinct second kanjis. (Miyazaki is also an incredibly common name!)
The fact that this murder seems to have some level of planning would indicate, to me, that if that were the motive they at least would have checked that, as opposed to hearing it on the street and going into a frenzy.
In the 1st thread there should be a link to the Japanese boards
@Incoherent has posted. There is a story of someone who posted as the “killer.” While I think the story is fake, two things stayed in memory.
1) the liberating, almost euphoric, feeling that the killer described
2) him mentioning his whole family being killed by one of the Miyazawa family ancestors
Now, I personally feel that the killer didn’t have a solid motive, just wanted to kill, and any motive would be secondary
But also, if we go down that rabbit hole, it is not a grandpa that was killed by another grandpa in WWII, it is the whole family that has been mentioned so maybe it was a big tragedy, something like what had happened in Nanking, for example, where the whole family could have died and a child survived
We are tying the ancestral family of the murderer up to Korea because of these archaic genetic tests interpreted by TMPD, but the family could have lived anywhere, and i think if something happened during the war, it was a civilian settlement that had been occupied
I think the killer was looking for a “souvenir”related to family photos; he either didn’t find it or thought it would implicate him too much and dropped the idea
Now, even if it was a “pretext” for the killing, time-wise, it could have been any of the four lines, maybe even eight, so Miyazawa is not the only one to study
IRL, for a pretext, the murderer doesn’t need this specific family, any Japanese person would be “the archetype of a Japanese invader”, and in life, the murderer chooses the most defenseless ones. But, in case he is caught, he has to have a convincing story, so maybe people in his family did perish during the time of militaristic Japan. Again, the real motive is his urge to kill. JMO, honestly, he didn’t have a motive…
I suspect, though, that in his own line, there may be some victims of the tragic Asian history of the XX century, especially if he comes from Korea or, say, Manchuria, but (my family ancestor spent several years in Gulag, so I know how “familial memory” works) - it is a pretext, and even if your ancestor was a victim, you don’t mete out revenge on his descendants, it is asinine.
What I can also see is that it is neither a Buddhist nor a Shinto mentality, because karma doesn’t work this way. One of the Big Three or an agnostic/atheist can subscribe to it.