Inuyasha and Sesshomaru are half brothers, They had the same father and different mothers. Is there a name for the relationship between Sesshomaru’s mother and Inuyasha?
Stepmother, assuming she and the father are married.
Not necessarily. If Sesshomaru’s mother was the first wife, and Inuyasha is the son of the second wife, then English has no name for the relationship between them.
There’s not enough information in the OP. The culture from which Inuyasha and Sesshomaru comes may have a term for the relationship which does not depend on the order of marriages, or which accommodates concurrent marriages, or non-marital relationships. But we haven’t been told what culture that is.
What UDS said.
And BTW, ‘Inuyasha’ and ‘Sesshomaru’ are really cool names. I hope they are genuine names, whatever culture or part of the world they come from.
This is indeed the case.
I agree! But that’s unlikely, as they’re characters in the (quite excellent) Inuyasha manga/anime series. Inuyasha transliterates as “dog demon” (which he is one), and Sesshomaru as “killing blade”, where he has one that does (and one that doesn’t). So unlikely.