The short answer is no.
Incest is a taboo in Japan just like everywhere else (cousins are considered a little differently from the way they are in the US, but I don't know details).
It's not really the same thing as dealing with same-sex relationships, which don't seem ever to have been criminalized in Japan to the extent they have been in say the US.
All the angst in Onegai Twins about who is related to whom stems from the fact that none of the characters want to cross the line into an incestuous relationship.
Most anime about "incest" are similar: they deal with characters living in the same household or family who are attracted to each other and fear they are blood-related (or know they are not blood-related but are uncomfortable about getting into a relationship because they live under the same roof).
I can't tease out whether all of this is just something to hang a plot on (to drum up angst and tragedy) or if people find this titillating as a potential sexual situation (there is Japanese ero material which falls into the latter category); I am not interested in doing so.
I can name some shows I have seen which relate to this topic:
but even looking at the list may spoil some of the shows I guess, so I will put a
*************SPOILER WARNING************ here.
I can't think of any more or didn't see them. Anyway, it's at least a partial list and an answer to your question.