
SPOILERS................................................................................................................................................................................................................................................................................................................................................................................................................
the taran bloodline:
only relatives can birth a male taran. be it a sister or cousin, as long as the male and female are related, the child born is always gonna be a son.
outside the taran bloodline:
the only way a taran male can impregnate a non-taran female is when the female has been treated. the treatment is exactly lucia's situation. female needs to consume some herb when she gets her very first menstruation. she needs to consume this herb every period until she stops bleeding. after that, she needs to drink some medicine that will make her fertile again. then she can have sex with the taran male to get impregnated with a female child.
no other situation will result in pregnancy except the 2 above.
Hue hates his bloodline because he finds the incest disgusting.
MORE SPOILERS BELOW
taran family history:
the male taran will impregnate a relative. a son is born. the same male taran will impregnate a non-taran female and then a female child is born. this female child, which is the half sister of the son, is gonna be the son's bride. as soon as they are of age/ deemed mature enough, the female and male children marry and then birth a son. the guy looks for non-taran female and births a female to create a half-sister cum bride for his own son. then the cycle continues.
i don't know if i remember correctly but usually the female taran is a half-sister of the male since they only get pregnant once, so cousins are scarce. Hue's situation is unique since he has a twin brother. the dead twin brother has a son (who is gonna be introduced as Hue's son) because he fell in love with his sister (he doesn't know she's his sister).

i actually like this development. as much as i hate drama/misunderstandings, i want this to happen so yuki will have an idea about how naruse feels when she's with hakamada. i don't think this situation will actually get out of hand, i don't see sunohara getting the feels back for naruse (or if she does, i don't think she'll attack), she seems like a good girl. the only way this situation is gonna snowball is because of the black haired friend lol
Is like an awkward Claude ( ̄∇ ̄") hahah but he looks more like an older Anastacius