This is a pretty good story so far. My concern is is that at some point I hope that the SI will have that realization that he did not just characters from an anime, but actual people. It’s just the way that he sometimes writes off people saying that “oh yeah someone else have them” like they’re nothing more than trading cards kinda makes him come off as a bit of a douche bag

Looking forward for the next chapter to come out soon

Looking forward for the next chapter to come out soon

what bullshit, so he is only average high-class devil in power output despite touki power of destruction, which means his demonic power reserve are only middle-class, then Issei transfert his power and he can reach Satan-class, are you kidding me.

it doesn't make sense that Zeroth is exhausted in his special form, as he only coat his body with his aura, and doens't borrow it unlike Vali, Issei or Sairaorg's ability. So rather than time limit, he should be able to control that form as long as he is focused and has enough power to maintain it.

Issei doesn't have enough magical power to boost his demonic power several times and transfert it to grant enough power to Zeroth to deal with Kokabiel if Zeroth's full-assault wasn't enough to even injure him slightly. You don't seem to understand Sairaorg's original power level or the power of destruction. Sairaorg without Regulus can display feats equal to an average Ultimate-Class Devil, or at least the top-tier of High-Class Devil. He has the physical abilities to keep up with Kokabiel, that is also a warrior by boosting them with his Touki, that further increases his speed. Even if slower, at least, he should be able to keep up to some extent. With the Power of Destruction focused on his fist, it should deal more damage than just the level of a High-Class Devil's average attack, as it is a more destructive type of energy, so more efficient in terms of damage output and magic power, though because of Kokabiel's satan-class power, he still must unleash his full power. As it is an attack controlled as an aura, it isn't extinguished or explode, and is always compact, so he can maintain it and channel it without wasting extra energy and can keep fighting much longer. Furthermore, the energy can be focused, so the sheer quantity of aura of destruction in a small technique would increase its destructive power, unlike only releasing it as a blast. It should at least keep up with Kokabiel's light sword or damage the skin of Kokabiel and maybe penetrate Kokabiel's aura, even if the power of the fist isn't enough to harm him, it can still dissolve his skin/aura.
The reason why Vali had an easy fight was because his demonic power are on par with an Ultimate-Class Devil (eight Devil wings as proof), and he was in his Balance Breaker, so his physical abilities and magic power were enhanced by Albion's dragon aura. His Sacred gear also has wings specialized in speed, so his flying speed should be higher than other winged beings. He is also strong enough to halve Kokabiel's power and absorb said power without releasing it, so a single touch was enough to overcome Kokabiel. It isn't a matter of power, but rather technique. Divine Dividing is really strong against strong and single opponent, and its full power is displayed if the user has enough capacity to absorb the divided power.
Well, it doesn't make sense that Zeroth cannot even damage kokabiel with his full power, or can even recuperate his demonic power, life-force and stamina so fast and still be a threat to kokabiel with a few boost of Issei, that is reputed for his low demonic power. It would be something else if issei was able to boost himself in his Balance Breaker, where he channels Ddraig's dragon aura.

if he used all his power in this attack and Kokabiel didn't protect himself well, it should deal more damage than Rias' attack did. In addition, his demonic power should be nearly depleted and his vitality and stamina too (by unleashing all of his life-force with it).

transfert can be used to transfert's issei's boosted power, but due to his low demonic power, he can only transfert the equivalent of an average high-class devil or two at best, rather than doubling Zeroth's power, so at this point in time, it isn't enough to deal with Kokabiel

he doesn't need to be on par in terms of magical power with kokabiel to damage him, if not how could most fighters in dxd defeat their enemies. Unlike Issei that is an armor-type, Kokabiel can be damaged by Zeroth if he is as strong as Sairaorg power of destruction. With the same amount of magical power, he can display greater damage output, and his physical abilities are not inferior to high-level warrior. Of course, he is still inferior to Kokabiel in terms of power, and can only damage him by unleashing most of his power at once a few times, so he must make it count by attacking towards his neck, heart, or any fatal parts.

to be fair, if he is on par with Sairaorg his strength should be equivalent to an ultimate-class devil. By using his Balance Breaker, Sairaorg was shown to be on par with Satan-class, and in Breakdown the Beast, he was above Satan-class, maybe God-class. As such, Zeroth should be able to rival his power level, and with the power of destruction, if he focuses it enough, he should be able to harm a Satan-class opponent such as Kokabiel, so his fighting chance isn't at zero even without Regulus, but he would still need to fight with all his power without reverse, unleashing large portion of his demonic power in each attack. Indeed, even Satan-class opponent don't release all their power in a single attack, so if an enemy with one or two level below attack with their full power, they can still be harmed even if they protect themselves. he can also focus his power to attack the heart, head, throat, or anything fatal rather than Kokabiel's whole body. Kokabiel has more magical power but Zeroth can use 2 types of energy to increase his power level and reduce the difference to some degree, as well as use the power of destruction, which is a more destructive type of demonic energy. In other words, by using 1 mp, he could maybe deal 10 or 50 damage, whereas Kokabiel would only deal 1 or 2 damage with that same amount and would need more energy. One of the reasons why the Bael Clan is OP is because even if their power is below their enemy, they can still rival them in attack and defensive power. Of course, if Zeroth is injured by light, he would be poisoned and receive more damage, in addition, the light would also attack his soul and cut down his stamina, life-force and demonic power, so it is important for him to avoid damage from Kokabiel if he want to win, but if he coat his body with the power of destruction and touki, unless Kokabiel focuses his power and bypass the area where he gathered most of his aura (fist), he can still do it.

Rizevim can negate the abilities and attacks of Sacred gears, so he can only do it with his own power.

Yo still waiting for the next chapter to come out soon

Looking forward for the next chapter to come out soon. For Valerie Tepes to be able to use the holy grail for combat. If I remember correctly the grail only brings mental damage to its user if they are trying to bring back the dead. But if the user is bringing back souls for communication purpose then the strain only goes on the user mana to maintain the soul appearance in the material plain. So my suggestion is using earth magic to make golems for the souls to occupy so that they can fight Valerie enemies. Or option 2 which is human transmutation since the holy grail has power over life itself there is no chance of Valerie meeting with truth from fullmetal alchemists. You can make use of the devil magic to make option 2 possible because devil magic relies on the user imagination. Which will make it easier to do the human transmutation using devil magic to make magic circles to summon forth the materials used for human transmutation. If it's still not clear where I'm going with these. It would be like Valerie summoning servants from fate series temporarily to fight for her. Like I said reviving the dead equals brain damage. But summoning souls equals heavy mana usage. Personally I recommend option 2 because using option 1 will make the summoned servant heavy because of there body made of rocks. Please think about it.

Looking forward for the next chapter to come out soon.

I mean lion form is more or less golden. I hope kuroka gets a golden haired mode just as a gag.