I don't remember how the beginning went but what I do remember is

-Kagome went through a ritual she changed into a demoness/or Half demoness
-ritual was extremely painful
-Kagome hair changes to a gray color
-Kagome and sesshomaru are siblings after the ritual but later Mates
-ritual was originally for rin but it would've killed her
-demon pregnancy's are extremely long and painful and all demons on protective of the childen
-Kagome gives birth in a dog position
-Sesshomaru's mother help with the ritual
-Kagome goes to some kind of huge library
-I read this on fanfiction.net
-I think it might've been rated M but I'm not 100% sure

If you could help me find this fanfiction I would love you forever lol I would really appreciate it if you can help me even if you can't find it
Thank you

It's not sounding familiar but do you recall if it was a recent story? Older? Complete??

It was an older story but it wasnt too old and I believe I read the story around 2015/2016 it was indeed completely Not sure if that'll help