That kinda sounds like the story I'm currently reading. Sesshoumaru finds Naraku in a cave and he begins to fight with him, but Naraku gets a specially made poison into Sesshoumaru's eyes that will slowly make its way into his brain and kill him. He then pierces Sesshoumaru trough the left side of the chest thinking that it will kill him, but Sesshoumaru's heart is on the right. Rin retrieves Kagome in order to help her Sesshoumaru-sama. His memory is gone but he's slowly remembering...
Its called
The Unexpected Twist of Fate by Psuedomonas. It's on spark. I think it might be rated R or M so just in case, no minors.