Whew! The story is up to 51 chapters, I really don't know where to begin, but I will try to summarize it quickly.
Kagome came back to the feudal era after three years to be with Inuyasha, and they were to be married. Sesshomaru was harboring feelings of lust and other emotions that he did not want to consider on, namely love. He manipulates Kagome to sleep with him and she does because she didn't have many options. Feelings develops on both sides afterward, but misunderstandings drove them apart. Inuyasha and Miroku were away for two weeks on demon extermination when Kags slept with Sessh.
She went back to Inuyasha and pretends that whatever happened between her and Sessh did not happen and marries Inuyasha. They try immediately to have children, only trying when he was human, because Inyasha wanted his children to live normal lives, he wanted human children. Anyhow the babies were born as puppies and all hell broke lose. Inuyasha abandons her, the pups get sick and she went in search of Sessh for he was their father and no one she knew could help her heal them.
Overall Kags and Sessh ended up bonding after many trials. Inuyasha returns five months later and put the pieces together, bitter and enraged he loses some of his sanity. He used a maturing Rin, raping and impregnating her. Abuses her emotionally and physically to spite his brother. And capturing Jaken in the process who was sent on a mission by Sesshomaru to gather information on his brother before he, Kagome and the children set out to find him, to dissolve Kags marriage so he can mate her.
A bunch of things happen, Sess almost died and he mates Kagome before she dissolved her marriage. They have more pups. Inuyasha hires mercenaries to go after his brother, fearful of him now that he had dishonored Rin, he prevents Rin from bonding with the baby, only letting her feed and cleaning her because she refused to be his woman. Jaken stayed with Rin even though he could have escaped, she was emotional and needed him.
The story is full of lemons and I swear that was not my original intent. I should be writing the last two chapters to end the story but I cannot because the killers that Inuyasha hired have a vendetta against Sesshomaru, and that is another story in itself. Sessh, Kags, and the children have met up with the first set of thugs. The story definitely cannot end in the two chapters now.
I fear that it is becoming drawn out, but if I end it in two chapters it would be shortsighted and inconsistent. The story is full of drama and unexpected twist that I will have to further write on and explain. I don't feel the passion for writing such a long ending. I hope that helps!