@Nk9bjP4A
his innate water rank is E.
it is E + SSS now because the sword upgraded the skill (since it is a powerful subject).
your question doesn't make sense, because for some reason you're considering his innate rank and his bonus rank at the same time.
for other people, it doesn't show his innate rank (which is E). That's why others see SSS now. It was SS before he acquired the sword. Your question should be "what is the difference between a SS vs SSS rank?", and tbh the power levels haven't been shown yet, so it doesn't matter