The fact that you were worried people might complain is your first clue that the ability is a bad idea (Sorry if that sounds rude, it's supposed to be a legitimate hosting tip) If you are ever worried something might be broken, overly complicated, or only balanced because of how the character uses it, there's a good chance it's not a healthy power and you shouldn't allow it in your RP
Also, last night when I wrote my post, I had no idea what Kakine's ability was. Strat said it defide the laws of physics, so I pointed out that he was the second strongest esper in existence. And the only one known to actually defy physics
It can't be undiscovered, because it exhibits two properties that cannot exist according to the laws of the universe:
A. It can deconstruct matter without releasing an excess of energy
Don't get me wrong, there are ways to deconstruct matter within the laws of the universe, but they all expel a massive amount of energy. Also, keep in mind that the only way to do this at a subatomic level is through nuclear fission. Technically to do it at an atomic level it could be a chemical reaction, but that would form new substances, rather than only ripping apart non-Substance A substances
But alright, Mugino does something close to this with her electrons, so maybe it's plausible. But even so, the next bit just doesn't work
B. It can convert deconstructed matter into itself
Okay, so, even assuming Substance A could somehow perform nuclear fission without causing a huge explosion, it then has the issue of having to put all those subatomic particles back together into it's own atomic makeup. So first it has to capture them and prevent them from shooting off as radiation. Then it has to compress them. And while compressing them it has to make sure they don't form into other non-Substance A materials (which the would be infinitely more likely to form due to the fact that Substance A is not a natural substance) And even assuming it could somehow, miraculously, do all these things, you then have to take into account that the absorbed matter might not create a balanced chemical equation when it's formed into Substance A. Leaving you with leftover particles causing all kinds of instability. It is possible to forgo this issue by deconstructing the matter a level further into quarks, but that just brings us back to the issue of how it can deconstruct matter
Due to exhibiting these properties that cannot exist in any substance in the universe, it must be a substance not of this universe
Which brings me to my next pair of points:
This ability is equivalent to Mugino's ability. It displays several extremely similar properties such as being able to destroy anything thrown at it. It is somewhat limited by its critical mass factor, but it's still extremely close and makes up for it with greater versatility. This alone makes it very plausible that the ability could only exist as a level 5 ability, which was stated to be something we couldn't have
This ability also exhibits properties so far only shown by the second ranked level 5 esper. I've already demonstrated why Substance A must be an exotic substance. And so far the only ability capable of legitimately creating a substance that can't exist within the universe is Kakine. This again suggests that it would be a level 5 ability. Although, again, it is lacking in some properties that prevent it from being exactly the same
But then you combine these two points and realize that it has properties somewhere in between that of the fourth ranked esper and the second ranked esper. Which presents an extremely strong case for why it would have to be a level 5 ability
And then you point out that the character doesn't like to abuse it, and I point out that Musujime was still on an equivalent level with Shirai even though Musujime is recorded as being less comfortable with using her ability than Shirai is. Level is clearly about the ability to do something, not the willingness
K, so, breaks physics, level 5, and one more thing. Although this is more of a mechanics issue than a logic issue
You never actually get rid of any of the mass. You say he has to re-absorb it, but then next time he uses his power it will still be at the same level of mass before he stopped using it. Basically, you never gave him any release, he sucks stuff in but it never goes back out
Alright, that should be everything. If you really want I can get into the more nitpicky stuff, but most of that can be handwaved so there's not much point to it