I wrote something like this before in another thread, just pasting it here.
Title: My garage is a portal to an Isekai without any sentient inhabitants, It's a free real estate! Did I mention I also found oil and other natural resources? [1]
Demographic: Mostly Shounen, maybe a little bit of Seinen
Genre: Action [2], Comedy, Drama, Isekai, Philosophical, Psychological, Sci-Fi [2]
Theme: Military [2], Office Workers [2], School Life [2], Survival [2]
Story idea:
Setting: Takes place in modern time, the year doesn't matter as long as the technology is at our level(e.g. Nukes, Internet, the ISS, iPhone) AND the current worsening of climate change, I haven't decided which country this takes place with, my country of preferences be either: Japan, USA, or Indonesia [3]. I'm not even sure if the "real world" setting should be our Earth though, I'll leave this on the discretion of whoever that wants to adapt this. Hence you may create entirely fictional countries or planets as the "real world" setting, as long as it maintains the trait of our world and bonus for containing the traits of the 3 previously mentioned countries. The "empty isekai" (temporary name), should truly be uninhibited from sentient species, there may be native animals and plants, though try to skip the troublesome part like diseases or other ecological disasters [4] by handwaving or something.
Main Character: So the MC will be male and shounen-like, I don't have an age yet but preferred to keep him in range of 14-28, Can't begin naming him before figuring out where the setting takes places, but I'll help pick a symbolic name if the culture has been decided. Family? Haven't decided yet, but he'll be a single and virgin at the start. Since his age is still tentative, his incomes at the start of the story are undecided yet, but he should have ample enough resource to kick start the business of exploiting the empty isekai.
Some of his characteristics: I think it's normal to explain his flaws first just like most manga, he dislikes money, dislikes hard labor, is selfish (on short term), bad at communicating, impatient, and indecisive (on short term). He likes Science, Philosophy, Psychology, and 2D stuff like Cartoons, Comics, Anime, Manga, Games, etc. But he doesn't live in 2D since he actually longs at the vast universe of the 3D world. He recognizes the threat of climate change that will ruin his dream of exploring the vast universe, he also dislikes paying for 2D stuff and basically pirated them, but at the same time is also sympathetic to the creators of 2D who also require earnings to make a living. He longed at creating a utopia where everyone including creators and consumers to be fully provided with necessities so they may enjoy doing what they do, as a secondary dream. In contrast with his bad communication skills, he is good at listening, deep thinking, not being dense, great memory, and understanding the nature of problems and how it came to be. This story may have a Grey on Gray morality though, so the MC may do questionable deeds for the "greater good" of his vision, but considering Death Note is considered Shounen, I think that's fine.
Plot: I think I overwrote the other sections leaving this one quite predictable eh? So MC finds a portal to the empty isekai in his property, the portal doesn't have to be a garage, but something large enough for a car to get in and out [5], and then he decides to exploit this empty isekai that's rich with natural resources. Keep it a secret from several evil organizations and stuff, starting businesses to dominate the market with exploits from the empty isekai, use money so he can exploit the empty isekai better, have a goal to create a utopia, save the "real world" from climate change, and start extensive space exploration program. You know that kind of stuff, you could almost tell that I got many of the ideas from Dr. Stone.
[1] The title is subject to change, but you can get the general idea from this one.
[2] Not sure if they're even needed to be tagged here, but at least some elements of them will appear here and there.
[3] Japan, because of his character, how he came to be, some of his lighter goals make more sense to be there, and maybe a bit more economic advantage for his rapid developments in the exploiting of empty isekai to make sense. The USA because of good geography and greater market competition leaves open to more stories about the market, also more potential actions and stuff. Indonesia because it's where I live, and I have greater knowledge and could give more flexible ideas.
[4] This may be expanded in the later story where either or both worlds are impacted by such disasters due to the other.
[5] There may be a possibility where we can upgrade the portal, like allowing larger size or more portal points as the story progress.
