User blog comment:B214/Volume 23 discussion blog/@comment-31137559-20170321042248/@comment-30048084-20170321184145

Remember there are rules that determine things I doubt the Maou decide promotions most likely there is a council that decides this.(maybe this is how Ishibumi thinking)

Issei rapid increase in ranks originates from not only his accomplishments but also his influence in the underworld's society, his power is also an extremely useful asset to the underworld.

Kiba is a mixture of factors not only does he possess a balance breaker that literally "breaks the rules of the world" he also has a decent amount of accomplishments on his side.

Akeno was Rias's first servant she has the powers of a not just a fallen angel but the powers of one of the leaders of the fallen angels and say what you want but she has shown herself as a powerful asset to the underworld.

I suspect that the second the tournament ends mass promotion letters will go out.

In regards to the Ultimate Class Devil thing I think we are underestimating what exactly equates to the rank of Ultimate Class Devils. Rias can fight a Ultimate Devil is impressive but it would be expected of her because she possess the power of destruction and is the little sister of Sirzechs. Issei can't become a Ultimate Class Devil because his quick ascension to High Class Devil is a problem to the Pure Blood Devils if he jumps all the way up to Ultimate imagine the effects on the underworld.