Writing Quality
First of all is the writing quality, frankly, it's atrocious. The main problem is the fact that you tell not show. You're feeding us so much information in a inorganic way. It feels artificial and really funny. It feels and sounds like how an alien would perceive and write a book after a detailed summary of it.
The quality also suffers due to poor grammar. This looks like a 4th grader wrote this. You know what, that's a bit harsh for 4th graders because at least they know how to do capitalization. You need to fix your grammar. It's also best if you get someone to help fix it for you if you can't.
Stability of Updates
Can't say anything since it's only been the first few chapters.
Story Development
It's not good. I didn't care for Wanwan's death. Why? Because you didn't give us time to care for her. In fact, I found the things leading up to that scene really funny. The dialogue was really funny. It was so forced and out of nowhere that it just ended up being comedic.
It feels artificial, as if it was written by a AI with a vague definition of human interpersonal relationships. We don't get shown things, but we get told things. We got told of Wanwan's relationship with Kakeru but we're not shown their relationship. It feels forced and doesn't make us care for these characters.
Kakeru's bullying is another topic I want to discuss. It encapsulates a lot of your problems. We're told of him getting bullied but not shown how he was bullied. Do you honestly expect us to care if we are just told that he is being bullied, and not shown how he was being bullied. It would have been a great topic to explore with the Isekai genre, but, personally, I don't think you're the right person to handle this. You are simply to inexperienced and *******ish of a writer.
My interpretation of the themes is that it's about escapism, fantasy, and avoiding one's own problems. Kakeru runs away because of the bullying. He avoids looking at people, literally, running away from eye contact. He runs away from a robber. He even wants to run away from his own world. It makes sense for an Isekai. Good job on that front.
(It's likely that you didn't even think about this if your writing skill is any indication.)
Character Design
There is none to speak of. You aren't taking advantage of the perspective you use. If it was in first person then you can't really describe the clothes of a person unless they're a character that's new to the protagonist. In third person it's a different story. In that perspective you take the role of a narrator. It means that you can describe what the characters are wearing.
World Background
We got an unappealing exposition chapter right from the start. It wasn't intriguing, it was boring and doesn't serve to push the plot forward. It should've picked up right when Kakeru is already in the fantasy world. Isekai can do organic worldbuilding well because the protagonist doesn't know shit about the world. You didn't need to put the whole first chapter when it can be better served as a interaction with Kakeru and his eventual harem.
Conclusion
You need to rewrite this. This is plagued with problems that can't be fixed in later chapters. I suggest the aforementioned rewrite or get someone to be your editor.
