One common illusion in MC light novels could be the illusion of power. The main character might seem weak at first but then reveals hidden strength, giving an illusion of a sudden power-up. For example, in some novels, the MC appears to be an ordinary person in a magical world, but later it is discovered that they have a special bloodline or ability that was hidden all along.
The illusion of choice can also be present. Sometimes, the MC seems to have a choice between two paths, but in reality, the outcome is already somewhat predetermined by the author. This gives the readers an illusion of multiple possibilities, but as the story unfolds, it becomes clear that the 'choice' was just a part of the overall plot design.
Another illusion could be the illusion of identity. The MC might pretend to be someone else for various reasons. This creates an interesting plot as other characters interact with them based on the false identity. For instance, the MC might disguise as a noble to infiltrate a high - society event in the light novel's world.
Authors also use misdirection to create illusions. They might introduce a character or a plot element early on that seems important but is actually a distraction. For instance, a side character who seems to be a key to solving a mystery but is actually just a red herring, creating an illusion of a more complex mystery.
One popular 'badass mc' is Kirito from 'Sword Art Online'. He's highly skilled in combat within the virtual world and shows great determination.
One popular 'badass mc light novel' could be 'Overlord'. The main character in it is extremely powerful and has a very cool and dominant presence. He rules over his domain with an iron fist in a new and strange world.
One popular merchant mc light novel is 'Overlord'. In it, the main character has a merchant - like approach in managing his territory and resources in a new world. Another could be 'Reborn as a Space Mercenary'. It features a protagonist who uses business acumen in a space - themed setting. There's also 'Myne the Bookworm' where the main character's actions in the world of books can be seen as having merchant - like qualities as she tries to preserve and spread knowledge which has economic implications in her world.
One popular OP (Overpowered) MC (Main Character) Asian light novel is 'Sword Art Online'. The main character, Kirito, is extremely powerful and his adventures in the virtual world of SAO are full of action and drama. Another is 'Overlord'. In this novel, the MC Momonga is a very powerful sorcerer who gets trapped in a game world and has to navigate through various challenges with his overwhelming power.
One could be 'The Cold-Hearted Mage's Ascent'.
Another might be 'No Game No Life'. The protagonists are highly intelligent and seem to have almost god - like abilities when it comes to games. The story is full of strategic battles and interesting world - building which is a common feature in good light novels.
The main character's ruthlessness. It makes the story more exciting. Readers like to see a character who can take decisive actions without hesitation. Also, the plot in 'ruthless mc light novel' is often full of twists and turns, which keeps readers hooked.
It's difficult to determine its popularity. Just because we haven't seen it widely promoted doesn't mean it isn't popular among a certain group. It could be that it has a small but dedicated fan base that really enjoys the unique concept of the mc being forced to drink 'liquid x'. Maybe it's new and just starting to gain traction, or it could be an older title that has been overshadowed by more mainstream light novels.
I'm not aware of a specific 'mc as robot light novel' to base similar recommendations on. But some general robot - themed light novels could be interesting. For example, 'Full Metal Panic!' has elements related to mecha and robots, though the main character isn't exactly a robot but has a lot to do with them.