One popular 'isekai ojisan light novel' could be 'Isekai Ojisan: Isekai ni Tensei Shita Kedo Cheat Nanka Shinai yo'. It tells an interesting story about an uncle who gets isekai -ed but doesn't have the typical cheat skills.
I'm not sure who the main characters are exactly as I don't know this work well. But from the title, it seems that a bishoujo and an ojisan would be important characters.
I'm not entirely sure as I haven't read it in detail. But generally, it might be about some sort of fantasy story involving a bishoujo (a cute girl character in Japanese media) and an ojisan (uncle or older man) in a novel - like setting.
Typically, in these kinds of novels, the main character is the person who gets transported to the other world and has a background in pharmacy. Alongside them, there could be a sidekick or a mentor figure in the new world. For instance, a young apprentice in the new world who is eager to learn from the protagonist's knowledge. There may also be antagonists such as jealous local healers who feel threatened by the protagonist's new - fangled pharmacy methods.
I don't know for sure since I haven't read this specific novel. But typically in an isekai story, there's a protagonist who is transported to the other world. So it's likely there's a main character like that in this 'isekai shikkaku novel' too.
In a generic isekai novel, the main character is typically someone who feels unfulfilled in their original world. In the new world, they meet various characters. There are friendly locals who befriend the protagonist and help them on their journey. There are also otherworldly creatures, such as elves, dwarves or magical beasts. And there are often guild members. If the new world has a system of guilds, the protagonist may interact with them, like joining a guild of adventurers to make money and gain experience.
I'm not sure which specific 'isekai nonbiri novel' you're referring to. Different novels in this genre could have a wide variety of popular characters. It could be a hero with a unique power that helps them navigate the new world.