I notice on his character page it is listed as streams of energy but I thought it was fire. I know your saying well what would be the difference between Yamamoto's and his? Here is what I think, Yamamoto's fire seemed more like hellfire you know. Even his techniques have hell in them. His name is even a reference to the hindu God of death Yama who is seen as the ruler of hindu version of hell. I see the flames that Isshin produces more like holy flames. I think that can also be seen in their color which im judging from his getsuga tensho are a light bluish white color. I mean isshin's release command is burn, I just don't think that is energy running on his blade but holy fire which is a complete opposite to Yamamotos hellfire and may have a different texture than normal fire. What about you guys, what are your thoughts.