Try
The Price of Vengeance by Youkai Fate
SesshouMaru has always despised his hanyou brother and seeks to avenge the insults InuYasha has paid him. But is he willing to pay the price of vengeance? S/K I/S K/K M/K M/F Lemons NEW CHAPTER UP!
Posted : 2004-05-05 -:- Edited : 2006-11-11 00:00:00 -
Rating MA and unfortunately incomplete.
Somewhere around chapter 30, Inuyasha and Sango were searching for Kagome who was kidnapped by Sesshoumaru. Inuyasha goes all demon-mode after fighting with Sesshoumaru and mates with Sango. There may have been rain involved, not sure.