Complex sentence: He once trained with Snake Eyes and had had a rivalry with him, but when Hard Master was murdered, Tomisaburo blamed Snake Eyes and swore to get even according to Storm Shadow's side of the story.
Split into simpler sentences: He once trained with Snake Eyes and had had a rivalry with him. But when Hard Master was murdered, Tomisaburo blamed Snake Eyes and swore to get even according to Storm Shadow's side of the story.