Single-handedly the longest arc in this manga. No that it's a bad thing tho. We've been waiting for this since the beginning of the manga. I think Ren is a great take of "the strongest". She has unrivaled power but, her biggest weakness is her ego. Of course if anybody had powers that rivals gods (even surpasses them) they'd have a god complex/massive ego. Before meeting Yuuki, she had a MASSIVE (Low Taper Fade) and stable ego. But, after the "reward" she gave Yuuki, her ego has started to crack. I mean being the ''STRONGEST" and getting humiliated by someone way weaker than you, you would start to be petty towards that person. Plus, she is the Commander of the MDF, meaning all her orders must be followed, she would abuse this power. If she does win or get her hands on Yuuki she'll probably try and humiliate him, only to be humiliated herself.