That's not as bad as if you marry a widow(er), and then your father marries your daughter-in-law.
Then, because your new mother-in-law's parent is married to you, you'd then become your own grandpa (or grandma)
Well, you could go back in time, accidentally get your grandfather nuked, and then sleep with your grandmother while trying to help her grieve...
It's because I was with Sanae for her proposal practice all day yesterday...I-I see...'Morning, Letty!'Morning, Suwako. You look sleepy.If Sanae and Yuuka get married...Mm-hm.Degrees of Kinship...won't that make you my daughter too?Uh, won't I be your sister...or niece?Both of your families are way too complicated.But...