Originally Posted by Kraco
I had forgotten all about the explanation in Index about Touma's power. Damn loli teacher talking too much. Well, that solves that issue. So, in fact Touma doesn't probably need to suffer any damage as long as whatever energy coming still has magical properties.
Another matter is how long he can keep doing it. That in itself would at least be one factor in gauging his theoretical level.
I don't really know why he wants to keep it a secret, though. It seems to me people in that academic city place lots of importance on the power level (making Misaka almost an idol, for example), so why does he want to appear a zero level failure?