Huge plot in the story is how many people are afraid that MC may become derange and start murdering everyone. Looking at how unstable and stupid he is currently, there is actually a possibility that story might take that path. Also because his followers hide a lot of stuff from him, it also might be a factor. Honestly, the more you read this, the more disappointing it becomes.
One of the biggest disappointments for me was how Seoyoon started to speak. She was exchanging notes with MC because she was too shy one moment and then in the next paragraph she was working in a restaurant talking to a bunch of strangers. WTF? Huge deal was made of how she was able to communicate only with him and then sudden jump to complete cure. Such a missed opportunity for a good chapter.
gets involved with the king, defeat dragon god, wipe out army of 10 thousand in front of the whole city, creates new magic that thought to be impossible before in front of the king and other people, etc
Basically the final boss is way to strong and has too many tricks so MC and the whole freaking human race has to get sudden power boost. And the ending of the battle is just idiotic overall.
Marring the girls just because they told him to is also stupid. Especially the princess who forced herself on him, then gets jealous even though he said "no" originally.
Making establishment of a new kingdom boring must be a special gift of the author.
The reasons are 1) MC is too OP. There is never a feeling of danger or any tension. His companions are also never in danger 2) All problems are solved in a boring way. He only uses 2-3 magics, somehow he just becomes expert in martial arts even though he never trains. 3) Whatever the situation is, there is always some kind of deus ex machina ready.
1) When assassins attacked his home and the fairy killed them all, he thinks that they all left by themselves after she asked them politely because she said "they all left". Even though right before that she told him there are assassins and no one will miss them when they are gone and locked him in the room while she was killing them. For real? Mentality of 5 year old from 94 year old.
2) When he increases his mana to ridiculous amount, and people are telling him "wtf, your amount of mana is 10 times normal magician should have", he still thinks that he does not have that much mana. He also thinks that he is average in strength even though he is OP and that everyone around him should be the same. If he just looks at people around him, he can realize what kind of freak he is, and yet he does not.
3) His sword. Not only he trades a higher level artifact sword for the lower level artifact katana, he does not even freaking suspect anything. When his katana starts to perform above normal sword, he does not investigate it at all and just chills out still thinking it is a normal sword.