@TTX
While his family disowning him may not happen, society as a whole would probably judge him.
The dragons are rare and most people don't necessarily know a lot about them, especially the way they reproduce.
As such, the many people are going to think that he's some asshole who screwed up, got a girl pregnant, and now refuses to take responsibility.
In Japan, there is a stigma against illegitimate children. It was only in
2013 that they got rid of a law that made it so children born out of wedlock would only receive half as much in inheritance compared to those born in wedlock. (Presumably if the parent in question hadn't actually written up a will, and the inheritance was being decided by the state)
On the flipside, the stigma is softening, as evidenced by the fact that the reforms went through. Said reforms had first been suggested by the Legislative Council of the Japanese Ministry of Justice back in
1996, and were strongly opposed.
Japan isn't unique in having such a stigma:
-In some areas of Africa, the equivalent of flipping someone the bird is to point the palm of your hand towards them and spread all five digits, with the meaning being "You have five fathers", a.k.a. you're illegitimate because nobody knows who your real father is.
-Until 1983, being illegitimate was considered by the Catholic Church to be an impediment to ordination or receiving Holy Orders, meaning a man who was illegitimate needed to gain special permission if they wanted to become a priest, and anyone who was illegitimate needed special permission to become a monk or nun (Granted, part of the reason for these rules were because, in the distant past, noblemen often sent their illegitimate sons off to become monks or priests, so the rules were meant to prevent the Church from becoming a dumping ground for the illegitimate children of nobles).
-Becoming pregnant out of wedlock is one of the many things that can cause so-called "honour" killings.
-The word "bastard" and its equivalents are considered insults in many languages.