Okay so, I'm sure that a few people already have this theory but I haven't seen it and I just wanted to write it down:
Gunha (the #7 level 5) is a holistic esper
Spoiler for Evidence:
First of all we should note that Gunha is a gemstone, as in he wasn't turned into an esper by Academy City. Now it's possible that gemstones can only turn into AC espers, but as there hasn't been anything saying that I am going to assume that they can be either.
The second point is that nobody can explain what Gunha's power is, even in a city thirty years ahead of everybody else. Even he can't explain it. I think the reason for this is that they are all looking for the wrong kind of power. They (and he) are looking for a microscopic power, while he has a macroscopic one. They are trying to find his power the same way that they would find any other power, looking at the microscopic changes. However he's actually making macroscopic changes. As a result they can't figure out what his power is no matter how hard that he tries.
Thirdly note that a lot of characters from side stories have become more important in New Testament (Birdway, Ollerus, Brunhild, etc)
Now the first point against this theory is that Othinus went to all that trouble to prove that holistic espers exist, so why would she need to if there was one already? The answer to this is that she simply doesn't know about him. As for why Ollerus knew about it but she didn't: well Ollerus say anything about it until they actually fought iirc so it's entirely possible that he just recognized it as they fought, and not liking Othinus very much he neglected to tell her.
Another point against the theory is that Gunha was trained by the Kihara research institute, so when Kagun found out about the holistic esper why didn't he put two and two together? Well there are two possibilities to explain that: the first simply being he never worked on Gunha. He was a teacher for a while before he left AC so it's possible he wasn't working there when Gunha was there. Or even if he was he just never got the chance, his field of study didn't have anything to do with that and there are thousands of other Kihara's after all. Secondly even if he did work with Gunha and put two and two together, then it's entirely possible that he didn't tell anybody just so that he could put together the fight with Byouri. He was very dedicated to getting to fight her on even ground, and he knew that the testing scenario would be the perfect opportunity to fight her.
So that's my theory and evidence. What does everybody think?