User blog comment:MarineroLelouch/Power Ranking and Classes./@comment-24066070-20140211083758/@comment-24066070-20140211183718

The reason I say they can't be ranked is that most battles between these chars are decided by details. Some say Ren is weak with no durability, but he can remove the oxygen from an area. Even a powerful fighter would struggle if he/she is caught in such a situation, let alone the fact that fire shouldn't be able to exist in said situation. So looking at it that way, one could say Ren beats Natsu, since he can cancel out all his fire.

Besides, the serie has already shown "weaker" chars beating "stronger" chars, most notable example: Aria defeating Makarov. Common sense would say this is impossible and Makarov did get back at him, but Aria can beat him using the element of surprise.