Yep, that's correct. I'll post the exact wording of the strengths/weaknesses chart, just in case:
Weak to: Lightning and Water. Lightning can defuse the detonation process while Water itself can be used to either contain it or counter it. In the case of the specific Clay Variation of Blast Release, Fire can be used, also, to either Melt the Clay (in the weaker applications) or "cook" it, in the same way as one does with RL Clay, turning it to rock.
Strong to: Earth and Wind. Earth can't contain the explosions and is weak against them while Wind is ineffective to control or contain them.
So looks like there is only one C-rank for you to learn out of the four c-ranks. We'll do more jutsu per post as this training moves forward.
Just a controlled explosion in the palm of your hands, used as a way to hurl back small attacks or power-move on your opponent and break their weapon xD
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How might you use this jutsu in your fighting style?