Since I'm not well - versed in Yuta Tanaka's light novels specifically, it's hard to say for sure. But in general, light novels often have simple yet engaging language, vivid characters, and unique story settings. His works might also follow these trends.
Cursed fanfiction is a type of fan - created writing that often contains very strange, disturbing, or unconventional elements. It might involve combining characters from different universes in really odd ways, or putting them in situations that are completely against their normal character traits. For example, making a cute and friendly cartoon character into a villain in a very dark and twisted story.
It's hard to give an exact time as it depends on the manga's plot development. But typically, Yuta Okkotsu shows up when certain events and character arcs lead to his introduction.