the actual God of Calamity/who resurrected Izumi/why did the Gods abandon this world/the "existence" of Yata of this world with the parelled one, etc

Also, this is not really a dungeon building novel. The MC is simply stuck in his dungeon. He wanted to live his life freely and wanted to venture out of his dungeon by his own will but he was turned into a Demon King was restricted by the God of Calamity to advance her research regarding the original (presumably to defeat her original based on her final words as she is a replica).

Excluding Kurokiri, the three characters that I considered main characters as well are Ichiko, Ryo and Izumi. Ichiko and Ryo purpose are to revolt and vanquish Kurokiri who turned them into demons which their intentions has changed by time, Ichiko has fallen in love with Kurokiri by time and although Ryo do not harbor any intention to kill Kurokiri anymore in the latter part of the story, her intention has shifted from killing him to regaining her freedom. As for Izumi, you can read the next spoiler, but there is a MAJOR spoiler there, it's better not to read it if you plan to read other Outer World Story series.

Izumi is a prominent character in the Outer World Story series. She makes a lot of appearances throughout other Outer World Story series. Her personality is very serious perhaps due to her childhood experience or due to Kurokiri's influence. Her initial intention is to repay Ichiko who has saved her life but her intention has changed throughout other Outer World Story series when she found out her brother's soul is trapped when he died and she decided to be a God to search for him.

like how author try to tell us that MC is so good at setting trap and build up dungeon but you won't see much detail in his management except saying that he's so good at it or preparation is perfect that make me feel that it's more about his op characteristic that he get by chance since there also no detail in MC paste or anything and refer to his characteristic as demon king

also that op cheat that he could just take anyone as his kin without their agreement that is make thing become more half-heart and those character seem to act in killing human so easy too

- at this point I don't found much management which I expect from dungeon management genre, instead author put in op evolved insect monster that even military's mage spend all of their mana into firemagic but it still deal just 1 dmg

- too convenient setting and progress, even through Japan acknowledged MC's dungeon to be most dangerous one but somehow they still send few 6 people squad to die in his dungeon once in awhile, also condition to escape dungeon is too convenient for demon kings since invader need to stay at least 1km away from entrance and over 1 hour have to pass before they could leave dungeon

- this one is only my taste but I feel disgusting when I found MC toying a girl (human which turn into his kin by his cheat) by s*xual harassment to get her information report (her family is in important position so she could sneaky get those information from her house which in area near MC's dungeon, so very convenient isn't it -_-")