As of the current manga chapters, Sanemi is still alive. His character has gone through many challenges but has managed to survive. The plot continues to unfold with him as an important part.
There could be a situation where a biker was in a crowded area, like a biker rally. There was some sort of misunderstanding or rivalry. Maybe one biker thought the other was disrespecting him or his group. Tensions built up, and instead of using fists, one biker impulsively headbutted the other. However, to really know the full story, we need more details such as the location, the people involved, and what led up to that very moment.
Since I don't have specific details about this 'sanemi light novel', it's hard to say precisely. However, in many light novels, the plot often includes elements such as a unique setting, be it a fantasy world or a post - apocalyptic one. Sanemi might be at the center of a mystery or a power struggle. There could be a love interest involved too, which could add an extra layer of complexity to the story.
I'm not sure specifically which "motorcycle headbutt" story you are referring to. There could be various incidents involving motorcycles and headbutts in different contexts, like in a motorcycle race where a rider might accidentally collide and there could be a headbutt - like impact. Without more details, it's hard to tell the full story.
You can find sanemi fanfic on some well - known fanfic platforms like Archive of Our Own (AO3). There are tons of fan - created stories about Sanemi there. Another place could be FanFiction.net, though the selection might be a bit different. Some fandom - specific forums may also have links to or host sanemi fanfic.
The main character is Sanemi. Depending on the type of light novel, there could be a group of characters around him. For instance, if it's an adventure - themed one, there might be fellow adventurers who each have their own skills and personalities. There could be a healer in the group who takes care of Sanemi when he gets injured, or a strategist who helps plan their next moves. And then there might be a mysterious character whose true intentions are not clear at first, but as the story unfolds, they turn out to be either a great ally or a formidable foe.