I'm not entirely sure as I haven't read it specifically. But generally, a light novel often has a unique story line, perhaps with complex characters and an interesting world - building. It might involve the adventures of the characters, their growth, and the challenges they face in the world of 'ultimate kars'.
I'm not familiar with the 'ultimate kars light novel' in detail. However, in most light novels, there are usually a protagonist and antagonist. So, Kars is likely the protagonist. As for the other main characters, there could be someone who opposes Kars, perhaps a rival with a different ideology or goal. There may also be characters that are important to Kars's development, such as a family member or a love interest.
It could be Harry Potter himself. He already has many extraordinary qualities like his ability to resist the Killing Curse. In fanfiction, he could be further developed into an 'ultimate life form' by gaining more powers, such as the ability to fly without a broom or to instantly heal any wound.
Well, it could be about a character achieving an ultimate life form through some unique training. Maybe they discover a new chakra mode that transforms them into an ultimate life form with incredible powers like super speed and strength.
A common theme is power exploration. Since Sonic is the ultimate life form, many fanfictions focus on his powers, how he got them, and how he uses them. For example, some stories might show Sonic learning new ways to control his speed or strength.
In Harry Potter fanfiction, the 'ultimate life form' could be a being with combined magical abilities from different species. For example, having the strength of a giant, the intelligence of a ravenclaw wizard, and the shape - shifting ability of an animagus all in one. It might also possess immortality, which is a highly coveted trait in the wizarding world.
Percy Jackson would likely still be a main character. He has such a central role in the original series that it's hard to imagine a fanfiction without him. Another might be Annabeth Chase, as she's Percy's close companion. There could also be new characters created specifically for this fanfiction, like a mysterious ultimate life form character who becomes Percy's ally or adversary.
It could also be a new character entirely. A young genin who is overlooked by everyone but has a secret power within. This character discovers a way to become an ultimate life form and uses this newfound power to make a name for themselves in the ninja world, challenging the established power structures and heroes like Naruto and Sasuke.
It depends on the specific context and the author's intentions. Sometimes, it might be considered canon, but without more details, it's hard to say for sure.