User blog comment:Jopjopjop/Volume 20 Spoilers/@comment-121.54.32.168-20150720122914/@comment-3477384-20150720125314

I don't have problem with him fighting strong opponents, and thus becoming strong, i have problem with how insanely fast the whole thing happens.

He was a human, a weak human. And in only 6 months he came the strongest young devil of the underworld, which Sairaorg trained for years.

That's why i feel it would have better if things happened in a slower place, because in this form it feels like to me that Issei is only strong because he is the MC, and not because he trained for it. (I still don't think that training in your free-time, for 1-2 months could show the same results as Sairaorg training, in normal circumstances)