Is "腹違いの兄" considered a slur? Is "" currently considered a slur? What about with past generations in Japan? In US society at least it once had negative connotation. But, now there is no negative meaning at all. What about Japan? What is the formal way to say ""?

The formal and neutral way of saying this is or .

is slangy, but not derogatory in itself in most cases. Some people may feel it's politically incorrect or vulgar, and use the alternative expressions.