I'm not sure specifically as it's not a widely known novel to me. It could potentially be about using magic to control or open up an isekai (another world). Maybe it follows a protagonist who discovers this magic - related to isekai control and embarks on an adventure in a new world.
Since the details of this novel are not known to me, it's difficult to determine the main characters. However, in a typical isekai story with magic involved, there could be a young hero or heroine who discovers their power to control the isekai. There may also be an antagonist, perhaps someone who wants to misuse the power of the isekai or stop the protagonist from using their magic - based control. And of course, there could be various side characters like fellow adventurers, magical creatures, or wise old sages.
I'm sorry, I haven't read this light novel specifically. But generally, 'isekai' often involves a character being transported to another world. If it's controlled by magic ('seigyo mahou de'), it might have a unique magic system and adventure plot in the other world.
The themes could include adventure and exploration. The idea of using magic to open up or control an isekai world implies that there will be a lot of unknowns to discover. There might also be a theme of friendship or camaraderie. In this new world, the protagonist may meet various characters and form bonds with them. Also, the struggle between good and evil could be a theme, as in many isekai stories, there are often forces that oppose the protagonist's actions in the new world.
I'm not entirely sure as I haven't read this novel specifically. But from the title, it might be about an isekai mage who is unable to use magic. Maybe it's about his/her struggles and adventures in the new world without relying on magic powers.
I'm not sure about its popularity. It might be popular within the niche of isekai and harem - loving audiences, but it may not be as well - known to a broader readership.
There's not enough information available to determine the author of this novel. It might be a new release from a small press or even a self - published work, so it's difficult to say who wrote it without further research.
The title 'isekai de kojiin wo hiraitakedo novel' is rather mysterious. 'Isekai' implies a different world, often a fantasy setting. 'Kojiin' is likely a name or a specific term in this context. 'Hiraitakedo' which might be related to opening or starting. So the novel could be about a story where in this isekai world, there is a character Kojiin who is on a quest that involves some form of opening, perhaps opening a portal, a chest, or even opening up new relationships or opportunities within the world of the story.
I'm not sure specifically as I haven't read it in detail. But generally, 'isekai' often involves a character being transported to another world. 'Harem' usually implies a story with a male lead and multiple female characters in some sort of relationship. So it might be a novel about a character in an isekai setting with a harem - like relationships.